Techniques for Tagging and Tracking ... - Wiley Online Library

North American Journal of Fisheries Management 20:597–609, 2000 q Copyright by the American Fisheries Society 2000

Techniques for Tagging and Tracking Deepwater Rockfishes RICHARD M. STARR* University of California Sea Grant Extension Program, Post Office Box 440, Moss Landing, California 95039, USA

JOHN N. HEINE

AND

KORIE A. JOHNSON1

Moss Landing Marine Laboratories, Post Office Box 450, Moss Landing, California 95039, USA Abstract.—Using scuba in August and September 1997 and 1998, we surgically implanted acoustic transmitters (Vemco V16 series) in 6 greenspotted rockfish Sebastes chlorostictus and 16 bocaccio S. paucispinis on the flank of Soquel Canyon in Monterey Bay, California. In 1997 we used longline gear to capture and tag greenspotted rockfish, and in 1998 we worked with a commercial fisherman who used modified trolling gear to help us capture and tag bocaccio. Each year, fish were captured at depths of 100–200 m and reeled up to a depth of approximately 20 m. This depth was chosen to reduce temperature and pressure stress caused by bringing fish to the surface. A team of scuba divers descended to the 20-m depth and anesthetized and surgically implanted acoustic transmitters in both species of rockfish. Tagged fish were released on the bottom at the location of catch. Several weeks after tagging, we used the Delta submersible to place an array of recording receivers on the seafloor, which enabled tracking of horizontal and vertical movements of tagged fish for a 3-month period. In September 1998, scientists and pilots were able to relocate three of the tagged fish by using a hydrophone on the submersible, which enabled them to navigate to the middle of schools that contained the tagged fish. Tagged fish were tracked for a 3-month period and provided information about the movements of the two species.

Rockfishes Sebastes spp. are an important component of the commercial and recreational fisheries on the U.S. West Coast. Fishing effort and landings of rockfishes have increased significantly over the last 40 years (Pearson and Ralston 1990), and there are now indications that abundance and size composition for several species are decreasing (Pearson and Ralston 1990; Karpov et al. 1995; Pacific Fishery Management Council 1995; Ralston 1998). As a result, fishery management for rockfishes is becoming increasingly complex, and areaspecific management strategies, such as the use of marine reserves, are being considered as a way to conserve stocks (Yoklavich 1998). The effectiveness of spatial management techniques, however, is dependent upon the rates of movement of the protected species. Because knowledge about fish movements is important to evaluate the efficacy of area management strategies, we developed techniques to tag and track rockfishes inhabiting water depths of 100–200 m, which we define for this study as deep water.

* Corresponding author: [email protected] 1 Present address: National Marine Fisheries Service, 501 West Ocean Boulevard, Suite 4200, Long Beach, California 90802, USA. Received July 19, 1999; accepted January 16, 2000

In traditional tag–recapture studies, fish are brought to the surface, tagged with an external marker, and released. Researchers then wait for tag recoveries via the commercial or recreational fishery (e.g. Mathews and Barker 1983; Culver 1987; Stanley et al. 1994). Such studies provide longterm movement data but little information about short-term movements. Acoustic tracking systems have been used for more than 20 years to identify short-term movements of fishes (Stasko and Pincock 1977), especially for freshwater species. Matthews (1990a, 1990b) was one of the first scientists to use acoustic systems to track shallow-water (,50 m deep) rockfishes. She brought copper rockfish Sebastes caurinus, quillback S. maliger, and brown rockfish S. auriculatus to the surface from a depth of 25 m or less, tagged them externally with sonic transmitters, and successfully followed them using scuba and surface tracking equipment. Results provided information about the differences in seasonal habitat use of several different species and age groups. Despite the successes of tagging shallow-water species, the methods of sonic tag attachment and long-term tracking are problematic for deepwater species. Traditional tag–recapture studies that bring fish to the surface place a great deal of stress on fish with closed swim bladders. A large com-

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ponent of this stress is caused by the barotrauma associated with rapid decompression. Typical barotrauma symptoms include everted stomachs, cloudy eyes, eyes bulging from orbits, and distorted flesh and scales (Parrish and Moffitt 1993). Handling mortality thus can be exceedingly high when deepwater species with swim bladders are brought to the surface. Also, many rockfishes with inflated swim bladders have difficulty returning to the bottom, even after the swim bladder is punctured (Coombs 1979). As a result, few people have successfully tagged fish species inhabiting water depths greater than 50 m. Priede and Smith (1986) were able to deploy sonic tags and track fish for a few hours in a deepwater species by enticing abyssal grenadiers Coryphaenoides yaquinae to ingest sonic tags wrapped in bait. Parrish and Moffitt (1993) used scuba gear to tag juvenile Hawaiian snapper Pristipomoides filamentosus at depth; they reeled hooked fish to within 30 m of the surface where divers orally inserted the sonic tags. Pearcy (1992) also tried, with yellowtail rockfish Sebastes flavidus, to increase tag retention time for the oral-insertion method by adding barbed hooks to the sonic tags; retention times ranged from 2 to 89 d. Our goal was to place acoustic tags on greenspotted rockfish Sebastes chlorostictus and bocaccio S. paucispinis and track them for a 3-month period. To prevent tag regurgitation, minimize fish mortality caused by barotrauma, and eliminate infection caused by external attachment, we developed scuba techniques to surgically implant tags at feasible depths. In addition to problems of tag attachment, sonic tracking studies of fish movements to date have been limited by weather and logistical problems associated with tracking from a surface vessel. Therefore, we also developed techniques to place recording receivers on the seafloor for a 3-month period to obtain semicontinuous information about fish movements. Methods Tag experiment.—Before tagging the two rockfish species with sonic tags in the field, we tested three different attachment methods at the Monterey Bay Aquarium in Monterey, California. Acoustic tag dummies, with the same dimensions and weight of real acoustic tags, were attached to kelp rockfish S. atrovirens, gopher rockfish S. carnatus, olive rockfish S. serranoides, and vermilion rockfish S. miniatus in three different treatment groups: oral insertion, dorsal attachment to the musculature just below the dorsal fin, and surgical insertion

FIGURE 1.—Location of the Soquel Canyon study site in Monterey Bay, California, locations of fish release, and receiver locations.

within the abdominal cavity. A control with no tag attachment was included. Each attachment method was replicated five times. For each tag group, we assessed duration of tag retention, abnormal or hindered swimming behavior, weight gain or loss over a 6-week period, and the presence or absence of external skin irritations. Study site and fishing methods.—The study site is approximately 20 km west of the port of Moss Landing in Monterey Bay, California (Figure 1). It lies on the flank of the submerged Soquel Canyon in 100–250 m of water and contains benches with soft sediment and rock outcrops surrounded by steep sediment slopes and rock walls (Yoklavich et al. 1993, 1995). Commercial and recreational fishing for rockfishes is common in the area. General locations for sampling were obtained from known sportfishing locations and from previous sidescan sonar and submersible surveys in Soquel Canyon (Deb Wilson-Vandenberg, California Department of Fish and Game and Mary Yoklavich, National Marine Fisheries Service, unpublished data). During the first year, rockfishes were caught using two baited longlines deployed from a research vessel. During the second year, a commercial fisherman was hired to catch fish using modified trolling gear. The gear contained a 10–15-mlong monofilament line attached just above the down weight; jigs were placed about 1 m apart on 0.25-m-long leaders. A small float at the end of

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FIGURE 2.—Close-up view of the V-board attached to the surgery center, showing equipment used to tag deepwater rockfish: (A) hypodermic needles to bleed air from swim bladder, (B) external dart tag applicator with tags, (C) sonic tag, (D) scalpel and forceps, (E) surgical stapler, and (F) liquid antibiotic.

the line kept the jigs trailing the down weight at a uniform depth. In both years, differential global positioning system (GPS) coordinates of the catch location were recorded. In both years, fishing lines were retrieved at about 20 m/min, a pace slow enough to avoid decompression problems with the fish. Fishing lines were marked 20 m above the first hook, as an indicator to stop retrieval of the lines. Tagging gear.—After the longlines were deployed or while the fisherman was trolling, the tagging equipment was prepared for deployment. The surgery center used was an open-frame box approximately 2 m high 3 1 m wide 3 1 m deep. It was constructed of schedule-80 polyvinyl chloride and steel angle framing and equipped with a wooden V-board with Velcro straps to hold the fish during surgery (Figure 2). A 0.4-m2 flopper stopper was placed in the down-line of the surgery center to reduce movements caused by ship roll or pitch (Figure 3). Tagging tools attached to the surgery center included a scalpel, forceps, sutures, stapler, antiseptic bottle, acoustic transmitters,

Floy tags, and a tagging gun. A cage for recovery and release, approximately 1 m long 3 0.4 m high 3 0.4 m deep (Figure 4), where the fish were placed after tagging, was suspended near the surgery center. The cage was constructed of 1-cm rebar with nylon mesh netting around the frame. The down-line of the recovery cage also contained a 0.4-m2 flopper stopper to reduce movements caused by the ship (Figure 3). The cage was equipped with a tripping bar and two end doors that fell open when the tripping bar contacted the seafloor. The acoustic tags, Vemco V16 (Vemco Ltd., Nova Scotia) series tags, were 16 mm in diameter and 80 mm long and weighed 12 g in water. In 1997, tags had unique frequencies of 50–78 kHz. In 1998, we used coded telemetry transmitters that enabled us to put multiple tags on the same frequency. Ten frequencies were used, again 50–75 kHz. Transmitter power was 153 decibels re 1 uP at 1 m, allowing signal detection at a range of 1,000 m or greater under the sea conditions in Soquel Canyon. The transmitters had pulse widths

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FIGURE 3.—Schematic of diving operations used to conduct underwater surgery.

of approximately 10 ms and intervals of 10 s in 1997 and 10 or 16 s in 1998. In both years, tag life exceeded the length of time the moored receivers were in the water. Tagging operations.—To avoid swim bladder expansion and thermal shock to the fish, tagging was done below the thermocline, at a depth of about 20 m. While the fishing line was being retrieved, the surgery center, recovery cage, and a lightly weighted signal line were lowered over the side of the vessel (Figure 3). Once the fishing line was pulled up to the 20-m mark, the divers entered the water. Three divers were used: a surgeon who tagged the fish, an assistant, and a safety diver who monitored the entire operation and watched for predators. Divers were usually in hand-contact with one of the down-lines but did not use traditional tethered blue-water diving techniques (Heine 1986) because they had to move to different apparatuses underwater. The divers descended the fishing line and searched the first few hooks for rockfish of the appropriate species and size for tagging. If none were present, the safety diver gave one pull on the signal line to indicate to a deckhand to slowly pull up the fishing line. When a suitable fish was sighted, the diver gave a series of rapidpull signals to tell the crew to stop hauling up the line. At this point, divers checked the fish; if signs

FIGURE 4.—The recovery cage used to return tagged fish to the bottom; the rotating latches open the cage doors when the foot of the trip lever hits the bottom.


of excessive barotrauma were not present, the assistant surgeon, using a squeeze bottle with 10% quinaldine mixed with isopropyl alcohol, squirted the anesthetic near the mouth of the fish. Once the quinaldine had taken effect and the fish was relatively motionless, the assistant and surgeon removed the gangion and hook from the down line, and transferred the fish to the surgery center, where it was strapped ventral side up into the V-board. The gangion was clipped into a spring clip on the side of the V-board as a safety feature in case the fish wriggled free. Once the fish was secure, the swim bladder was bled with a small syringe needle if necessary, total length was recorded using a measuring tape affixed to the V-board, and surgery was performed. First, the scalpel was used to gently scrape the scales away from the abdomen, and a small incision (about 2 cm long) was made through the skin between the anus and pelvic fins, taking care not to cut into the organs below. Betadine antiseptic was squeezed into the incision to help prevent infection, and the acoustic transmitter was inserted. To help close the incision and keep the staples from hitting organs below the skin during stapling, the assistant pinched the skin around the incision with forceps while the surgeon closed the incision with three or four stainless steel staples. The surgeon then placed a Floy anchor tag into the musculature below the dorsal fin. In 1998, we changed to synthetic sutures to close the incision after we realized that the staples had pulled out of some of the larger fish. After surgery, the tagged fish was carefully transferred to the recovery–release cage, and the hook was removed from its mouth. Each fish was observed in the recovery cage for a few minutes to ensure it was sufficiently vigorous to release. Divers then swam back to the fishing line, gave a single pull on the signal line to restart retrieval and obtain more fish. The entire tagging operation took approximately 6 min/fish underwater, thus easily allowing for two to three fish to be tagged during one dive. When all divers and equipment, except the recovery cage, were back on board, the sonic tag was checked for proper function by deploying a hand-held omni-directional hydrophone attached to a Vemco model VR-60 receiver. Once we were assured that the tag was functional, and the frequency and depth transmissions were correct, the recovery cage was slowly towed back to the location where the fish was caught. As the cage was lowered to the bottom, depth signals were monitored to ensure the release system was working

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properly. The cage was assumed to be on the bottom when the deployment line appeared slack and the depth signals remained steady. The cage was raised 2–3 m and relowered to ensure the tripping mechanism properly functioned, then left on the bottom for a few minutes to allow the fish to swim out. As the cage was retrieved, the transmitter depth signal was closely monitored to ensure the fish was out of the cage and was not being pulled back to the surface. Fish tracking.—Vemco VR-20 subsurface receivers were the primary tools used to monitor fish movements. Using a Delta submersible, we tethered receivers to the bottom in both years with subsurface moorings (Figure 5). In the second year of the study, two receivers were deployed using an anchor and a surface buoy for short periods from August 17 through September 10, 1998, because tagging operations commenced 1 month before the submersible was scheduled to deploy the underwater moorings. These receivers were placed near the locations at which fish were released: the northeastern portion (site 1) and southwestern portion (site 2) of the study area. In 1997, to conserve battery power for the duration of the study, each receiver was programmed to turn on for 6 min and then off for 24 min in a continuous cycle. In 1998, receivers were programmed to turn on for 10 min each hour. For each tag signal heard, the receiver recorded the tag number, tag frequency, the date and time of signal reception, and the depth of the tag; in 1998, receivers also recorded signal strength, gain, and noise. During the submersible deployment of receivers, the pilot and observer first searched for an appropriate site to place the receiver. Care was taken to choose a site far enough away from the canyon wall and associated boulders to minimize acoustic shadows and close reflections that might affect signals reaching the receivers. Mooring anchors also had to be placed on relatively level substrates to prevent the receivers from being dragged down the side of the submarine canyon. When a suitable location was found, the differential GPS position of the Delta submarine was recorded and the mooring was released. The positions of receiver deployment were chosen to span the distribution of release locations of the tagged fish (Figure 1). In 1997, four receivers were placed on a ledge along the wall of the submarine canyon approximately 500 m apart on October 7 and retrieved by a remotely operated vehicle (ROV) on January 5, 1998. In 1998, six receivers were placed about 1,000 m apart on Sep-

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FIGURE 6.—Schematic of the canyon wall at the Soquel Canyon study site in 1998 and relative locations of hydrophones.

FIGURE 5.—Schematic of receivers moored to the ocean bottom at depths above the release depth of the fish. The receivers were inverted to minimize the chance of a signal reception shadow.

tember 16 and retrieved by ROV on December 30, 1998. Two of the receivers were located in about 100 m of water on the relatively flat bottom above the canyon rim. The other four receivers were placed in deeper water on flat shelves or gently sloping walls below the canyon rim (Figure 6). Approximately 3 months after deployment, the Monterey Bay Aquarium Research Institute’s ROV Ventana, and its support ship, the R/V Point Lobos were used to locate and retrieve the receivers. The receivers we used were omnidirectional; and a recording of a tag transmission indicated that the fish was within an approximate horizontal radius of about 1,000 m. To increase the amount of

information available, we placed the tagged fish and receivers along the side of a submarine canyon that trended northeast to southwest. Tag receptions of a given depth could not have originated from other areas due to the topography of the canyon wall. The resulting overlapping receiving zones of the receivers, combined with the depth transmission, reduced the number of possible locations of the fish and thus further defined the position and movements of the tagged fish. The Delta submersible was also used to verify that tagged fish were alive. We placed a Vemco VR-10 P high-pressure directional hydrophone on the bow of the submersible and fed signals to a VR-60 receiver operated by a scientist inside the submersible. At the start of a dive designed to locate individual fish, the submersible descended and rested on the bottom. The submersible pilot oriented the vehicle in a compass direction while the scientist scanned all programmed frequencies and noted signals from transmitters. After all 10 frequencies were scanned, the pilot rotated the submersible approximately 45 degrees and repositioned the vehicle on the bottom, whereupon the scanning procedure was repeated. The scientist scanned frequencies and noted signals at each compass bearing as the submersible was rotated incrementally in a complete circle. After the circle was complete, the scientist chose the strongest signal to follow from a tag that previously had not been seen. The submersible pilot


then slowly drove in the direction of that signal. As long as the signal remained strong, the pilot remained on a heading. If the signal started to become weak, the pilot repositioned the submersible on the bottom and rotated it left and right until the signal was again strong. By the end of the field season, pilots were able to make small course corrections as the submersible was moving by listening to the strength of the signal emitted from the VR-60 receiver. This technique enabled us to locate and observe tagged fish and verify they were alive and swimming in schools with other fish. Signal reception range.—In 1998, we placed four tags on the bottom for the duration of the study to use as references for comparison of signals from a stationary object and from a moving fish and to compare changes in range of signal reception with changes in temperature and salinity of the water. Tags on the bottom may not be recorded by the VR-20 receivers as far distant as tags in live fish because transmissions from a tag in the mud may arrive at the moored receivers as multipath signals and be rejected as nonvalid signals by the receiver software. However, they do provide an estimate of the frequency of electronic error associated with depth transmissions, indicating the effective range of the tags implanted in fish and the variability of signal strength recorded by the moored receivers. To test signal reception range, we compared the number of times a receiver was in its 10-min recording mode (‘‘bin’’) with the number of times a receiver recorded at least one tag signal in a bin for tags at known distances from receivers. Each receiver except number 2 was in recording mode 2,535 times from September 16 through December 30, 1998. Receiver number 2 was accidentally hauled up by a commercial fishing vessel October 26, 1998; thus, it contained only 961 recording bins. The results indicate that receivers recorded 80% or more of the transmitted signals when the tag was closer than 800 m (Figure 7), except when the tag was not in a straight line to the receiver. In cases such as with tag 6, which was located close to receiver number 6 but below on a steep slope at 185 m, the effective receiving distance was much smaller. To test depth estimates, we placed the reference tags on the bottom at known depths to estimate the precision of the depth transmissions. Pressure sensors in the tags allowed us to record depths of tagged fish (Figure 8) with an accuracy of 2% of the depth (Vemco, unpublished data). At a depth of 100 m, the accuracy of the depth was within 2

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FIGURE 7.—Percentage of the time that receivers recorded transmissions from transmitters placed at known distances away.

m, a value equivalent to the tidal range in Monterey Bay. More than 99.5% of the signals recorded from tag transmissions were within 2 m of the actual depth of the tag (Table 1), indicating that we could resolve vertical movements of the fish to within approximately 2 m, without correcting for tidal variation. Results Tag Experiment on Captive Fish Surgical insertion was selected as the best method for sonic tag attachment in rockfishes, based on experimental results of tag retention time, weight change, apparent behavior, and the extent that attachment incisions had healed (Table 2). We observed no mortalities or abnormal swimming in any of the treatment fishes. One dorsal Floy tag fell off after 2 weeks, and for all of the dorsally tagged fishes, the site of tag attachment was still raw and unhealed after 6 weeks. Fish with dorsal tags gained significantly less weight than the control fish (Wilcoxon’s signed-rank test, P 5 0.04). Three of the five fish with dorsal tags lost weight during the study. All but one of the orally inserted tags were regurgitated within the first 2 weeks, and those fish gained weight or remained stable after they had regurgitated the tags. All of the fishes with surgically implanted tags healed completely and had either gained weight or remained at a relatively steady weight after 44 d. There was no difference in weight gain between control and surgically tagged fish (Wilcoxon’s signed-rank test, P 5 0.69). Tagging and Tracking During the first year we successfully tagged and released 6 greenspotted rockfish 35 to 39 cm long,

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FIGURE 8.—Depth transmissions for a 1-week period in 1998 recorded from tag 7 in a bocaccio, showing the typical range of vertical movements.

and in the second season we tagged 16 bocaccio 35 to 58 cm long (Table 3). The time from placement of each fish into the recovery cage to the time the cage doors were tripped at the bottom ranged from 15 to 80 min. Two obvious mortalities occurred during the tagging process in 1997. In one case, the fish did not recover from the surgery to the point that we felt confident about its survival. In the other case, the fish was successfully tagged, but then accidentally brought to the surface when the recovery cage failed to open at the bottom. In 1998, we relocated three tagged bocaccio using the directional hydrophone mounted on a submersible. The fish were located in high-relief habitats with other untagged bocaccio. The schooled fish were actively moving both vertically and horizontally along the high-relief bottoms. In addition to the tagged fish, we were able to locate six transmitters on the seafloor, all were on flat, soft bottoms and sitting upright in fine, undisturbed sediment. Possibly, the fish died before the tag fell TABLE 1.—Frequency of signal receptions showing depths within 62 m of actual depths of tags located on the bottom. Tag number Depth (m) 2 6 8 11

100 185 90 97

Signals within 62 m of actual depth

Total number of signals

Number

Percent

15,514 854 9,316 19,078

15,495 851 9,313 19,074

99.88 99.65 99.97 99.98

out or a predator moved the tag; however, we believe the staples pulled out of live fish, causing the tags to fall to the seafloor, because we saw no evidence of scavengers around the tag and because we noticed that some surgical staplers did not work as well as others. We recovered two of the tags to implant in other fish, and used the remainder as reference tags. In the first year of the study (1997), a problem with internal cable connections caused a malfunction with one of the four receivers deployed. The three remaining receivers recorded data throughout the study in 1997 (Table 4). Signals from all tags, except tag 1, were recorded throughout the 1997 study period; the total number of transmissions recorded from each tagged fish ranged from 156 to 24,132. Signals from tag 1 were heard for 18 h, then not again until 67 d later. In 1998, the receivers placed on surface buoys in August and early September recorded continuously; total number of tag transmissions recorded for each of the tagged fish in that time ranged from 0 to 9,531 (Table 5). Signals from the 4 of the 16 tagged fish were only recorded on the day they were released or between August 17 and September 10. The six receivers that were deployed on subsurface moorings all functioned properly. The moored receivers recorded signals from 12 of the 16 tagged fish, with the total number of signals recorded for each tag ranging from 0 to 19,213 (Table 6). Elapsed time between a tag’s first and last recorded signal ranged from 1 to 140 d (Table 3). Receiver 1 recorded the fewest signals; it was lo-

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TABLE 2.—Results of tag experiments conducted in aquaria.

Rockfish species Gopher Kelp Olive Vermillion Mean Gopher Kelp Olive Vermillion Mean Gopher Kelp Olive Vermillion Mean Gopher Kelp Olive Vermillion Mean

Weight (kg)

Weight change Kilograms

Percent

TABLE 3.—Summary of tagging operations in 1997 and 1998.

Retention time (d)

Start

End

0.52 0.41 0.70 0.55 1.43

Control 0.58 0.06 0.55 0.15 0.84 0.14 0.56 0.01 20.08 1.35 0.06

0.52 0.60 0.59 0.82 1.43

Oral treatment 0.59 0.07 0.65 0.05 0.67 0.08 0.88 0.06 20.08 1.35 0.04

13.5 8.3 13.9 7.5 25.6 7.5

3 1 12 2 2 4

0.58 0.57 0.59 0.86 0.85

Dorsal treatment 0.59 0.02 0.59 0.02 20.01 0.58 20.05 0.81 20.26 0.59 20.06

2.8 4.2 21.0 25.8 230.9 26.2

44 29 44 26 13 31

0.60 0.66 0.62 1.10 1.97

Surgical treatment 20.02 0.58 0.15 0.81 0.16 0.78 0.03 1.13 20.01 1.96 0.06

23.3 23.1 25.7 2.7 20.3 9.6

44 44 44 44 44 44

Tag date

Date last signal (1998)

Tag FreTotal Release num- quency length depth ber (kHz) (cm) (m)

Delta time a (d)

Greenspotted rockfish 1997 Sep 17 Sep 24 Sep 24 Oct 16 Oct 17 Oct 21

11.9 36.4 19.7 1.8 25.60 12.8

cated at the northeastern-most portion of the study area (Figure 1). Receiver 4 contained the most recorded signals, but it was closest to the release locations of the majority of the tagged fish. Transmissions from tags 7, 18, and 25 were recorded by all receivers, indicating movements of fish across the study area. Discussion The results from our study indicate that surgical insertion is the most appropriate method for sonic tag attachment in rockfishes. Fish with surgically implanted sonic tags gained weight in experimental aquaria, indicating that feeding behavior was only minimally affected by the tags. Their incisions were closed after 7–10 d and were fully healed after 30 d. Our observations that some rockfishes rapidly regurgitated orally implanted tags and the weight gain of our experimental fish suggest that surgical procedures result in the least amount of behavioral change. This conclusion is supported by Lucas and Johnstone’s (1990) observations of tag regurgitation and Mortensen’s

2 3 6 7 10 1

57.0 60.0 67.3 72.0 78.0 54.0

37 38 39 35 35 35

220 232 204 160 160 144

b

111 104 104 82 81 67

96 95 98 95 106 140 99 99 98 92 92 95 95 95 96 96

Sep 5 Dec 30 Sep 9 Dec 30 Sep 8 Dec 30 Dec 30 Oct 5 Sep 1 Sep 20 Sep 2 Oct 11 Oct 1 Dec 30 Nov 10 Dec 30

25 140 28 139 15 128 122 36 1 18 1 13 3 93 42 92

Jan Jan Jan Jan Jan

5 5 5 5 5

Bocaccio 1998 Aug 12 Aug 13 Aug 13 Aug 14 Aug 25 Aug 25 Aug 31 Aug 31 Sep 1 Sep 2 Sep 2 Sep 29 Sep 29 Sep 29 Sep 30 Sep 30 a b

4 9 10 7 3 17 18 20 26 21 24 12 13 14 25 27

57.0 69.0 75.0 63.0 50.0 54.0 54.0 60.0 78.0 65.5 72.0 50.0 57.0 69.0 78.0 72.0

35 50 52 57 47 45 47 51 49 45 51 52 47 58 55 48

Number of days between release of a tagged fish and the last signal reception from that tag. December 26, 1997.

(1990) observation that stomach transmitters inhibited feeding more than ones imbedded in the visceral cavity. Similarly, Mellas and Haynes (1985) and Moser et al. (1990) reported that implantation of tags resulted in minimal behavioral change. The undetectable difference in fish behavior after surgical implantation of tags contrasts markedly to Pearcy’s (1992) observation that an externally attached tag caused one yellowtail rockfish to list to one side. The combination of fishing and diving from one TABLE 4.—Summary of the number of times each tag was recorded by each receiver (rcvr) when it was in receiving mode in 1997. Tag number

Rcvr 1

Rcvr 2

Rcvr 3

Total

1 2 3 6 7 10

44 2,726 944 1,968 2,252 1,960

73 10,766 4,404 10,754 2,658 3,667

39 10,640 4,240 11,193 1,551 1,135

156 24,132 9,588 23,915 6,461 6,762

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TABLE 5.—Summary of number of times tag transmissions were recorded by receivers temporarily placed in the study area early in the study period in 1998 (see text for description of location of site 1 and site 2). Tag number 3 4 7 9 10 17 18 20 21 24 26 a

Site 1

Site 2

Total

135 186 9,523 9 3 143 2,537

5 59 8 1,556 1 0 18 0 473 1 0

140 245 9,531 1,565 4 143 2,555 0 473 1 0

a a a a

Receivers were not programmed to record signals from tags 20, 21, 24, or 26 at site 1.

vessel proved to be logistically difficult. Low catch rates using hook-and-line gear and variable time between fish capture for each angler made it difficult to conduct efficient diver operations. Thus, we used longline gear in 1997 to improve efficiency by enabling divers to remain at depth and remove fish from hooks as the longline was retrieved. We also simplified fishing operations in 1998 by working with a commercial fisherman using modified trolling gear that was very effective at selectively catching bocaccio. It was similar to trolling gear used for Pacific salmon Onchorynchus spp. in the region (Starr et al. 1998) but contained a heavier down-weight and had different jigs. Working with a second vessel in 1998 enabled us to focus efforts on dive operations, rather than di-

viding our attention between catching and tagging fish. The troll gear also was more efficient to work with underwater than the longline gear used in 1997 because all the hooks were concentrated in a small distance and divers did not deplete air reserves as they did when waiting for the longline to be retrieved. On several occasions, we saw California sea lions Zalophus californianus at the surface feeding on rockfish that probably came off the fishing lines. A few sea lions also attempted to take fish from the fishing lines during dive activities. Blue sharks Prionace glauca may have also eaten a few fish because the fishing gear occasionally returned to the surface missing hooks. According to local fishers, blue sharks commonly remove hooked rockfishes from their lines during August and September in Monterey Bay. When fish were caught and slowly reeled to a depth of 20 m, the methods developed for diving in open water were very reliable for performing the underwater surgery. Although surgical operations were successfully completed by two divers, we believe a three-person dive team is required to safely and efficiently conduct the tagging operations. The safety diver was essential to monitor dive activities of the surgeon and assistant, actions of potential predators, and overall conditions of the dive, thus enabling the primary divers to concentrate on handling the fish. The safety diver ensured the surgeon and assistant were not entangled in the fishing line or lines from the surgery center and ensured that all divers monitored their air consumption. The safety diver also carried a long stick

TABLE 6.—Summary of number of times each tag was recorded by each moored receiver (rcvr) when it was in receiving mode in 1998. Tag number 3 4 7 9 10 12 13 14 17 18 20 21 24 25 26 27 Total

Rcvr 1

Rcvr 2

Rcvr 3

Rcvr 4

Rcvr 5

Rcvr 6

Total

0 0 475 0 0 0 0 0 0 905 0 0 0 12 0 0 1,392

0 0 1,651 0 0 9 0 7 0 1,449 7 0 0 26 0 0 3,149

0 0 3,444 7 0 26 54 139 0 3,165 4 32 0 78 0 77 7,026

0 0 2,343 151 0 38 82 9,025 2,621 3,250 0 0 0 26 0 10 17,546

0 0 104 3,421 0 26 148 36 0 328 20 83 2 204 0 9,341 13,713

0 0 97 3,788 0 9 67 2 0 51 8 0 0 89 0 9,785 13,896

0 0 8,114 7,367 0 108 351 9,209 2,621 9,148 39 115 2 435 0 19,213 56,722


to keep aggressive sea lions at a safe distance. Although the stick was available to ward off blue sharks, they were rarely seen, seemed only curious, and posed no danger for the divers. Effects of barotrauma on captured fish seemed to be minimal when we retrieved the longline at a relatively slow rate. We chose a retrieval rate slightly faster than the recommended rate of ascent for scuba divers (Heine 1999). Almost no bocaccio showed evidence of barotrauma, and swim bladders were intact, whereas we had to deflate the swim bladder of most of the greenspotted rockfish we tagged. This prescreening of fish for surgery and postoperation evaluation enabled us to minimize mortalities caused by the surgery. Patterns of signal reception by different receivers demonstrated movements of fish back and forth between receiving zones in 1997 and indicated that the six tagged fish survived the tagging process. Tag transmissions from five fish were recorded over the entire time the receivers were in the water. Signals from the remaining greenspotted rockfish (tag 1) were heard for a short time and then not until the end of the study, suggesting movement of the tagged animal. Based on our experience in the first year of the study, we assume that the mortality rate was low in 1998 as well. We are unable to estimate or verify the mortality rate, however, because many of the tagged fish appeared to leave the study area. Signals from three of the tagged bocaccio ceased within 1–3 d, three within 3 weeks and two within a month (Table 3). These fish either left the study area, died and were swept deeper into the submarine canyon, or had tags that failed. Signals from three other tagged bocaccio were recorded for at least 6 weeks, after which signals ceased. Signals from those three fish (tag numbers 17, 20, and 25) were recorded again later in the study after an absence of 27, 126, and 14 d, respectively. The intermittent pattern of these signals indicates the fish were actively moving because signals from reference transmitters placed on the bottom were recorded during the entire study. Five of the tagged fish remained in the study area for more than 3 months and showed signs of movement based on the pattern of signal receptions by the moored receivers. Occurrences of receiver cross-talk in 1997 and 1998 also indicated movements of live fish. Crosstalk occurs when a tagged fish gets close to a receiver (e.g., within 0–50 m) and a tag transmission is recorded on two different frequencies due to

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signal saturation of the receiver. In 1997, receivers 2 and 3 each recorded cross-talk of signals from the same two fish (tags 2, 6) at several different times, indicating those fish alternately swam close to one receiver and at a later time swam close to a second receiver more than 300 m away. In 1998, receiver 5 recorded cross-talk from tag number 23 as it moved into and out of the proximity of the receiver. The technique of placing receivers along ledges on the side of a submarine canyon enabled us to refine the position of the tagged fish, but it also caused many acoustic shadows and echoes. The hard, steep walls that undulate along the side of the canyon may have occasionally caused echoes and an original signal transmission to coincide, preventing the receivers from recording a valid signal. Thus, some of the time bins in which the receivers were in recording mode contained no signals from nearby tagged fish. Some of the lapses were probably also due to the tendency of some rockfishes to take shelter under rocks as well. From the surface, we occasionally heard weak signals that were unusually high-pitched and sounded ‘‘tinny.’’ In other studies of shallow-water rockfishes, we have experienced the same type of reception for several hours at a time when fish take shelter under a rock or ledge. The signal returns to full strength and timbre when the tagged fish leaves the crevice. As fishing pressure on rockfish populations increases, managers are considering new conservation methods, including the use of area management and marine reserves. Marine reserves are considered to be effective ways to conserve populations of harvested species, especially sedentary rockfishes (Yoklavich 1998), and may possibly enhance nearby fisheries (Sladek Nowlis and Yoklavich 1998; Johnson et al. 1999). To maximize effectiveness, however, reserves should be designed to accommodate the life history patterns of rockfish species (Carr et al. 1998; Starr 1998). In this respect, understanding the home range and daily movements of rockfishes is critical to understanding of the value of marine reserves. To date, studies of home range and movements of deepwater rockfishes have been limited by problems associated with barotrauma caused by bringing fish to the surface to tag. The in situ tagging procedures we developed alleviated many problems associated with surface tagging. We were able to develop techniques that provided information about horizontal and vertical movements of two rockfish species during all hours and all days for

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a 3-month period. These techniques appear to be a promising means for studying movements of deepwater species with swim bladders and may provide the means for obtaining increasingly important information more about fine-scale movements of fishes. Acknowledgments A project of this complexity requires the help of many people. We would like to especially thank Fred Voegeli of Vemco, Inc., for his help with the electronic equipment, John O’Sullivan and the Monterey Bay Aquarium personnel for helping design the underwater surgery center and allowing us to conduct tagging experiments, and Jason Felton for helping us tag rockfish in 1998. We thank Dave Lindquist for his help in the tag retention experiment, Tom Williams for helping with surgical procedures, and the people who helped us catch the fish, especially Dempsey Bosworth from the F/V Beticia, and Lee Bradford, Joe Bizzaro, and Kate Stanbury. Aldo Derose designed and built the recovery cage. Jean DeMarignac helped configure the current meter. We thank the people who provided the ships and submersibles and their crew, including the ship operations staff of Moss Landing Marine Laboratories, Wayne Kelly of Alladin Charters, the crew of the C/V Cavalier, the pilots of the submersible Delta, Dave Slater and Chris Ijames, and the crew of the R/V Point Lobos and ROV Ventana pilots. Greg Cailliet graciously provided funding for added ship time and helped evaluate the data. We also thank Kirsten Carlson for scientific illustrations and Lynn McMasters for graphics help. Funding for this project was provided by the West Coast and Polar National Undersea Research Center, University of California Sea Grant Extension Program, and Moss Landing Marine Laboratories. References Carr, M. H., and ten coauthors. 1998. Working group on design considerations. Pages 143–148 in M. M. Yoklavich, editor. Marine harvest refugia for west coast rockfish: a workshop. NOAA Technical Memorandum NMFS-SWFSC-255. Coombs, C. I. 1979. Reef fishes near Depoe Bay, Oregon: movement and the recreational fishery. Master’s thesis. Oregon State University, Corvallis. Culver, B. N. 1987. Results from tagging black rockfish (Sebastes melanops) off the Washington and northern Oregon coast. Pages 231–240 in Proceedings of the international rockfish symposium. University of Alaska, Sea Grant Report 87-2, Fairbanks. Heine, J. N., editor. 1986. Blue water diving guidelines.

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