Postmortem Length Changes in Six Florida Fish ... - Wiley Online Library

North American Journal of Fisheries Management 29:1242–1252, 2009 Ó Copyright by the American Fisheries Society 2009 DOI: 10.1577/M07-197.1

[Article]

Postmortem Length Changes in Six Florida Fish Species Stored on Ice THOMAS C. CHESNES*

AND

RAYMOND E. WALDNER

Department of Biology, Palm Beach Atlantic University, Post Office Box 24708, West Palm Beach, Florida 33416, USA

CECILIA S. KRAHFORST Department of Biology, East Carolina University, Greenville, North Carolina 27858, USA Abstract.—Representatives of six species of fishes belonging to the families Lutjanidae, Centropomidae, Pomatomidae, Scombridae, Carangidae, and Sciaenidae were stored on ice for 6 h after being euthanatized, in order to assess postmortem length changes. Standard length, fork length (where applicable), total length using the relaxed caudal fin method, and rigor mortis were measured immediately after deaths and at 30 min intervals thereafter. Two species, lane snapper Lutjanus synagris and common snook Centropomus undecimalis, showed an increase in mean total lengths during the first hour after death. Common snook continued to increase in mean total length for the duration of the study, while lane snapper subsequently decreased. Declines in mean standard, fork, and total lengths also were observed in bluefish Pomatomus saltatrix, Spanish mackerel Scomberomorus maculatus, and Florida pompano Trachinotus carolinus. Minimal changes in mean standard and total length were observed for spotted seatrout Cynoscion nebulosus. There was little direct correlation between rigor mortis and length variation for any of the studied species. The observed length changes may have implications for both law enforcement personnel and anglers.

In the State of Florida the harvest of nearly all popular game and food fishes is governed by regulations designed to prevent overexploitation. Regulations include marine protected areas, closed seasons, bag limits, gear restrictions, and length limits that vary from one species to another and, in some cases, between areas. One potential problem may occur when fishes that just meet the minimum length limits at the time of capture may shrink to below the minimum legal length by the time they are later measured by law enforcement officers. Fishes regulated by minimum and maximum length (or ‘‘slot’’) limits may also pose a problem if they expand beyond the maximum allowable length. Thus, changes in fish length after harvest may result in costly fines and the incarceration of anglers who adhered to the regulations at the time the fishes were captured. If anglers knew how much, if any, change in length to expect after a fish’s capture and storage on ice, they could determine how large a fish would have to be in order to adhere to the minimum and maximum legal length limits. Similarly, enforcement officers would be able to better assess whether an angler had intentionally harvested a fish protected by law. However, few studies have focused on length changes in fishes after * Corresponding author: [email protected] Received November 7, 2007; accepted July 28, 2008 Published online August 31, 2009

their capture, and fewer studies have involved fishes native to Florida’s waters. Several studies have investigated shrinkage in fishes subjected to storage in preservatives (Shetter 1936; Parker 1963, Stobo 1972; Lockwood and Daly 1975; Yeh and Hodson 1975; Jones and Geen 1977; Theilacker 1980), freezing (Halliday and Roscoe 1969; Jones and Geen 1977; Treasurer 1990, Armstrong and Stewart 1997), without any means of preservation or freezing (Morison et al. 2003), and storage on ice (Lux 1960; Halliday and Roscoe 1969; Rice et al. 1989; Gordon 1994; Blackwell et al. 2003). Only Rice et al. (1989) dealt with a common Florida marine fish: the spotted seatrout Cynoscion nebulosus. The purpose of this study is to determine if six species of Florida marine fishes belonging to different families change length when stored on ice after capture, and to quantify these changes in order to provide useful information for anglers and regulatory agency officers. Methods Species belonging to six families of perciform fishes were included in this study. These fishes were chosen due to their popularity as food and game fishes in the State of Florida, and because the State of Florida has established minimum length limits and, in the case of common snook Centropomus undecimalis and the spotted seatrout, maximum length limits for these species. Fishes included in this study were lane snapper Lutjanus synagris (family Lutjanidae, 12 specimens),

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common snook (family Centropomidae, eight specimens), bluefish Pomatomus saltatrix (family Pomatomidae, seven specimens), Spanish mackerel Scomberomorus maculatus (family Scombridae, nine specimens), Florida pompano Trachinotus carolinus (family Carangidae, eight specimens), and spotted seatrout (family Sciaenidae, nine specimens). Specimens were collected from 13 July 2004 through 11 April 2006, by using hook and line in the waters of Palm Beach and Martin Counties, Florida, USA. All representatives of Spanish mackerel, Florida pompano, bluefish, and one lane snapper were dispatched immediately after their capture, after which data recording began. All other specimens were held in a darkened, 95-L, flow-through live well and were dispatched shortly after their arrival at shore. In accordance with the rationale behind the ‘‘Guidelines for the Use of Fishes in Research’’ (Nickum et al. 2004), each individual was euthanatized by a sharp blow to the occipital region of the skull. Once dispatched, initially measured, and assessed for rigor, each fish was tagged by using a piece of numbered, waterproof paper secured to the caudal peduncle with copper wire. Specimens then were placed in a 66 or 114 L ice chest initially containing 18 or 37 kg of ice, respectively. Fishes were laid on the top of the ice in a single layer, to replicate the method that many anglers use to store their catches. The probe from a digital hygro-thermometer (item WW-74-9094, Carolina Biological Supply Co., Burlington, North Carolina) was placed on the ice beside the fishes to record the temperature and relative humidity within the chest during and between measurements, although the probe sometimes shifted position when the chest’s lid was closed. A 112 3 31 cm measuring board was employed to collect morphometric data. A stainless steel meter stick (model G339, Arthur H. Gaebel, Inc., East Syracuse, New York) with millimeter gradations was affixed to the board by using 5200 Fast Cure Adhesive/Sealant (3-M Products, St. Paul, Minnesota), and the zero point on the meter stick was aligned with a 10 3 31 cm vertical stop positioned at one end of the board. A plastic t-square (model 20002, Helix, Bensenville, Illinois) moved along the bottom edge of the board, facilitated alignment with the locations on the specimens from which measurements were taken, and allowed a high degree of accuracy and repeatability. The degree of rigor mortis attained by each fish at each measuring period was assessed by using the Modified Cutting’s Method described by Bito et al. (1983). Data collection began immediately after a fish’s dispatch and was repeated at 30 min intervals, for a period of 6 h. All length measurements were taken

from the anterior-most portion of the fish’s head with the mouth fully closed, as described by Hubbs and Lagler (1958). Data recorded included standard length, fork length (not recorded for spotted seatrout due to its slightly acuminate caudal fin), and total length, to the nearest millimeter. Total length was measured with the fish’s caudal fin ‘‘relaxed’’ rather than the ‘‘pinched’’ measurement described by Hubbs and Lagler (1958), as relaxed tail measurements were being used by law enforcement officers of the Florida Fish and Wildlife Conservation Commission (FFWCC) as well as several other states when this study began (the use of a ‘‘pinched tail’’ measurement for total length was adopted by the FFWCC during the course of this study). Anderson and Neumann (1996) noted that measuring the total length with fishes’ tails relaxed is a common practice in Europe, while pinching tails when measuring the total length is often used in the Americas. In this study, each fish’s caudal fin was gently spread by hand without forcing the fin to open, and the fin was then allowed to relax prior to taking the measurement. Linear regression was used to assess the relationship between changes in standard length and that of the calculated rigor index. Percent changes in length from each specimen’s initial measurement were calculated at each interval to allow a consistent basis of comparison among fishes of varying lengths. Linear regression models were also used to describe the trend line produced between percent changes in the length and the time elapsed. All statistical analyses were performed by using SPSS software (version 15.0). Results Temperatures within the coolers oscillated around a mean of 2.88C while holding fishes. Most of the temperature variation appeared to stem from the position of the probe relative to the bed of ice. Average relative humidity within the coolers was near 62% during the periods in which fishes were held. All fishes attained full rigor within the 6-h measurement period, with the exception of one lane snapper and two common snook (Table 1). Relationships between the degree of rigor mortis and the standard length changes were relatively weak or statistically insignificant (Table 1). Summary statistics for the initial measurements of all specimens are provided in Table 2. The mean total length of lane snapper showed an increase of more than 1.5% during the first hour of measurement. However, a 3% decrease was seen over the 6-h measurement period (Figure 1). Initial increases also were observed in both mean standard and mean fork lengths, followed by smaller (less than 1%) overall decreases in these

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TABLE 1.—Percent of individuals in full rigor at the beginning of each measuring interval. Linear relationships between rigor index and standard length are given. An asterisk represents statistically significant relationships. Rigor and Standard Length

Time (minutes) Species

0

30

60

90

120

150

180

210

240

270

300

330

360

r2

p

Lane snapper Lutjanus synagris Common snook Centropomus undecimalis Bluefish Pomatomus saltatrix Spanish mackerel Scomberomorus maculatus Florida pompano Trachinotus carolinus Spotted seatrout Cynoscion nebulosus

0 0 0 0 0 0

8 0 29 11 13 0

8 38 43 22 75 0

8 50 43 44 100 11

17 63 57 66 100 78

25 75 57 66 100 100

33 75 57 78 100 100

75 75 57 89 100 100

83 75 86 100 100 100

83 75 86 100 100 100

92 75 100 100 100 100

92 75 100 100 100 100

92 75 100 100 100 100

0.0455* 0.0145 0.1233* 0.1146* 0.0125 0.014

,0.01* 0.2239 ,0.001* ,0.001* 0.2593 0.2035

measurements over the 6-h period. All specimens of lane snapper decreased in total length, although some showed no change or even an increase in fork and standard lengths. In contrast to lane snapper, common snook increased by 1.2% in the mean total length over the 6-h measurement period (Figure 2). All but one specimen of common snook increased in total length over the 6-h period. A very slight increase also was seen in mean standard and mean fork lengths (Figure 2). Small declines (,1%) in mean standard, fork, and total lengths were exhibited in bluefish (Figure 3) as well as Spanish mackerel (Figure 4). Unlike the three aforementioned species, however, the least change in

Spanish mackerel occurred in the mean total length. The mean fork length showed the greatest change in Florida pompano (Figure 5), although this was still less than 1% of the original mean fork length. Minimal change was seen during the 6-h measurement period in mean standard and total lengths of spotted seatrout (Figure 6). Overall decreases were less than 0.5% for both measurements. Discussion Although changes were apparent in mean standard, fork (when measured), and total lengths of all of the species studied, those occurring in lane snapper and common snook potentially have the greatest effect on

TABLE 2.—Summary statistics of initial length measurements. Regulation lengths have been converted from inches to millimeters. Florida Regulations

Species Lane snapper Lutjanis synagris (N ¼ 12) Standard length (mm) Fork length (mm) Total length (mm)a Common snook Centropomus undecimalis (N ¼ 8) Standard length (mm) Fork length (mm) Total length (mm)a Bluefish Pomatomus saltatrix (N ¼ 7) Standard length (mm) Fork length (mm)a Total length (mm) Spanish mackerel Scomberomorus maculatus (N ¼ 9) Standard length (mm) Fork length (mm)a Total length (mm) Florida pompano Trachinotus carolinus (N ¼ 8) Standard length (mm) Fork length (mm)a Total length (mm) Spotted seatrout Cynoscion nebulosus (N ¼ 9) Standard length (mm) Total length (mm)a a

The measurement method used in Florida regulations. b Atlantic waters of Florida. c Gulf waters of Florida.

Range

Standard Minimum Mean Median deviation length

Maximum length

155–237 169.5 188–281 205.5 198–296 217

164 198.5 209

21.1 23.5 24.5

203.2

—

335–757 467 382–849 528.5 408–880 557.2

386.5 467.5 438

161.2 179.9 180.5

711.2

812.8b/838.2c

337–402 371.3 373–440 409.6 401–487 449.9

374 454 418

25.8 27.2 32.8

304.8

—

278–366 323.2 301–395 346.3 340–453 394

319 341 393

33.2 33.4 38.7

304.8

—

250–322 292 269–349 318 311–410 370.8

295.5 321.5 375.5

23.5 26.9 31.5

279.4

508

298–349 324 348–408 378.7

323 379.5

16.9 20

381

508


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FIGURE 1.—Percent changes in mean standard length (A), fork length (B), and total length (C) of 12 lane snapper over a 6-h period. Error bars represent range; trend line is a linear regression. The numbers of fish increasing and decreasing in length from the baseline measurement at each time interval are given above and below the baseline, respectively.

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FIGURE 2.—Percent changes in mean standard length (A), fork length (B), and total length (C) of eight common snook over a 6-h period. Error bars represent range; trend line is a linear regression. The numbers of fish increasing and decreasing in length from the baseline measurement at each time interval are given above and below the baseline, respectively.


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FIGURE 3.—Percent changes in mean standard length (A), fork length (B), and total length (C) of seven bluefish over a 6-h period. Error bars represent range; trend line is a linear regression. The numbers of fish increasing and decreasing in length from the baseline measurement at each time interval are given above and below the baseline, respectively.

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FIGURE 4.—Percent changes in mean standard length (A), fork length (B), and total length (C) of nine Spanish mackerel over a 6-h period. Error bars represent range; trend line is a linear regression. The numbers of fish increasing and decreasing in length from the baseline measurement at each time interval are given above and below the baseline, respectively.

fishery management and enforcement due to the magnitude of the changes observed in these species. Changes in mean standard and fork length measurements for both species were similar in slope and magnitude, but the mean total length measured by

using relaxed caudal fins—the measurement formerly used by Florida law enforcement officials for members of both Lutjanidae and Centropomidae—showed the greatest amount of change over the 6-h measurement period. These species have relatively flexible caudal


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FIGURE 5.—Percent changes in mean standard length (A), fork length (B), and total length (C) of eight Florida pompano over a 6-h period. Error bars represent range; trend line is a linear regression. The numbers of fish increasing and decreasing in length from the baseline measurement at each time interval are given above and below the baseline, respectively.

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FIGURE 6.—Percent changes in mean standard length (A) and total length (B) of nine spotted seatrout over a 6-h period. Error bars represent range; trend line is a linear regression. Numbers of fish increasing and decreasing in length from the baseline measurement at each time interval are given above and below the baseline, respectively.

fins that visibly desiccated and stiffened during the measurement period; this appeared to be the cause of the larger variation in total length observed in lane snapper and common snook. The decrease in the mean total length exhibited by lane snapper could lead to recreational fisheries violations for anglers who keep fish that just meet the minimum legal length limit. The increase in the mean total length of common snook can also pose enforcement issues within the State of Florida, since this species has both minimum and maximum (slot) length limits. Fish caught at the upper limit of the slot and kept on ice would become illegal if and when they lengthen over time. While the majority of sampled individuals for each species changed length in a given direction, a small number exhibited no change or even a change in the opposite direction (Figures 1 and 2). A lesser degree of change in the mean total length

was seen in the species with less flexible caudal fins; i.e., Spanish mackerel and Florida pompano. The linear regression slope and the magnitude of length change over time were minimal for these species. In Florida, length limits of these species are determined by a fork length measurement. Bluefish is also regulated by fork length measurements in Florida and, like the abovementioned species, only showed slight shrinkage in the mean fork length during the study period. Sciaenids are regulated by total length measurements in Florida. The change in the mean total length of spotted seatrout was extremely small (0.5%). These findings are consistent with the study Rice et al. (1989) conducted in Texas, which documented a decrease in the mean total length of 0.8% in this species. The change in the mean total length observed in spotted seatrout also appears to be due to a change in its caudal fin. In species where a change in the mean

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total length is most apparent (lane snapper, common snook, and bluefish), the slope of change over time is similar (and gradual) in the standard and fork length measurements. The trend lines describing the relaxed mean total length measurements are steeper and show the greatest degree of change. This is apparent whether the mean total length is decreasing (lane snapper and bluefish) or increasing (common snook). Caudal fin rigidity may be important in determining the extent of total length changes of fishes stored on ice. Larger changes in length have been documented in studies on other fish species. Specimens of lingcod Ophiodon elongatus, a commercial species from Alaska, were found to shrink an average of 6% of the dorsal length when stored on ice for 16–24 h (Gordon 1994). Fork lengths of European perch Perca fluviatilis and northern pike Esox lucius shrank 1.7% and 5.35%, respectively, after being frozen for 10–14 weeks and thawed before re-measurement (Treasurer 1990). Longer periods of cold storage may account for the greater magnitude of length changes noted in these studies. It would thus be wise for anglers who retain fishes at or near the legal length limits to keep the amount of time their catch is stored on ice to a minimum. Changes in the length of fishes have been attributed in part to the onset of rigor mortis (Natsume 1995), although this was neither strongly supported in the present study nor by Morison (2004). In addition, it was determined that the methodology used to document rigor in our study, as well as some others (Bito et al. 1983), was ineffective for larger fishes as their weight partially offset the ability of rigor to hold the body in a horizontal plane. If rigor did have a significant effect, this would be apparent in the standard length measurements. In this study, the standard length had the least degree of change in all species except Spanish mackerel. Interestingly, increases in mean standard, fork, and total lengths were seen in the first hour of storage of lane snapper, followed by a decrease in all measurements (Figure 1). Stobo (1972) noted this phenomenon in large yellow perch P. flavescens stored in formalin, and suggested body relaxation as a possible cause. A loss of muscle tonus may also be responsible for the initial lengthening of some fishes in the present study. Desiccation may have played a major role in fish length changes. However, as neither weight nor water loss was measured in this study, we cannot state this for certain. Freezing has been shown to cause a reduction in the weight and length of Atlantic cod Gadus morhua, haddock Melanogrammus aeglefinus, American plaice Hippoglossoides platessoides, and winter flounder Pseudopleuronectes americanus. When the fishes were thawed and allowed to soak in water for 24

h, weights increased but lengths changed very little (Halliday and Roscoe 1969). Desiccation and related weight loss were also noted when fish fillets were frozen (Boyd et al. 1967). The loss of moisture from caudal fins apparently was responsible for some of the changes in total length observed in this study. Increased length of storage time on ice resulted in the caudal fins becoming drier, stiffer, and more splayed. As a result, trend lines of standard and fork lengths were more similar to each other than to those produced by total length measurements (Figures 1–6). Thus, even though law enforcement officials in some states measure the total lengths by using relaxed caudal fins, this may be the measurement prone to the greatest variation over time and thus the least reliable measurement for regulatory purposes. Conclusion Length changes were observed in most specimens in this study. Anglers who harvest regulated fishes of a length at or near the minimum (or in the case of common snook, maximum) limit could potentially, over time, be in possession of an illegal catch. A harvested individual of lane snapper initially measured at a length of 204 mm, slightly larger than the minimum limit, could shrink approximately 6 mm if the length decreases at the average amount documented in this study. Likewise, an individual of common snook initially measured at 838 mm, slightly shorter than the maximum length allowed in Florida’s Gulf waters, could lengthen by approximately 1 cm, if it lengthens at the average value measured. In both instances, the angler would be in possession of an illegal fish and could be subject to penalty. Acknowledgments We thank M. Chesnes, M. Thomas, and B. VanDusen for assistance in specimen collection. L. Gregg (Florida Fish and Wildlife Conservation Commission) provided valuable assistance in obtaining collecting permits. J. Swick, R. Rulifson, C. Montague, and three anonymous reviewers provided invaluable comments. This study was partially funded by a Quality Initiative Grant from Palm Beach Atlantic University. References Anderson, R. O., and R. M. Neumann. 1996. Length, weight, and associated structural indices. Pages 447–482 in B. R. Murphy and D. W. Willis, editors. Fisheries techniques, 2nd edition. American Fisheries Society, Bethesda, Maryland. Armstrong, J. D., and D. C. Stewart. 1997. The effects of initial length and body curvature on shrinkage of juvenile

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Morison, A. K., I. W. Brown, and G. K. Jones. 2003. Post mortem shrinkage of four species of temperate and tropical marine fishes, without freezing or preservation. Journal of Fish Biology 62:1435–1449. Natsume, M. 1995. Shrinkage of fish body length by rigor mortis. Scientific Reports of Hokkaido Fisheries Experimental Station 47:1–6. Nickum, J. G., H. L. Bart Jr., P. R. Bowser, I. E. Greer C. Hubbs, J. A. Jenkins, J. R. MacMillan, J. W. Rachlin, J. D. Rose, P. W. Sorensen, and J. R. Tomasso. 2004. Guidelines for the use of fishes in research. American Fisheries Society, American Institute of Fishery Research Biologists, and American Society of Ichthyologists and Herpetologists. Available: www.fisheries.org (November 2007). Parker, R. R. 1963. Effects of formalin on length and weight of fishes. Journal of the Fisheries Research Board of Canada 20:1441–1455. Rice, K. W., R. K. Riechers, G. W. Standard, and J. E. Clark. 1989. Shrinkage of spotted seatrout held in ice. Texas Parks and Wildlife Department, Fisheries Division, Management Data Series 15:1–15. Shetter, D. S. 1936. Shrinkage of trout at death and on preservation. Copeia 1936:60–61. Stobo, W. T. 1972. Effects of formalin on the length and weight of yellow perch. Transactions of the American Fisheries Society 101:362–364. Theilacker, G. H. 1980. Changes in body measurements of larval northern anchovy Engraulis mordax and other fishes due to handling and preservation. National Marine Fisheries Service Fishery Bulletin 78:685–692. Treasurer, J. W. 1990. Length and weight changes in perch (Perca fluviatilis) and pike (Esox lucius) following freezing. Journal of Fish Biology 37:499–500. Yeh, C. F., and R. G. Hodson. 1975. Effects of formalin on length and weight of bluegill and white crappie from Lake Nasworthy, Texas. Southwestern Naturalist 20:315–322.