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Overwintering habitat use of shortnose sturgeon (Acipenser brevirostrum): defining critical habitat using a novel underwater video survey and modeling approach Xinhai Li, Matthew K. Litvak, and John E. Hughes Clarke
Abstract: The overwintering habitat use of shortnose sturgeon (Acipenser brevirostrum) was investigated from January to March 2005 in the upper Kennebecasis River, New Brunswick, Canada, using a novel underwater video camera system and modeling approach. Following a random sampling procedure, 187 holes were drilled into the ice, and 234 sturgeon were counted and video-recorded. We found that sturgeon concentrated in a 2 ha area at the confluence of the Kennebecasis and Hammond rivers on a flat sandy substrate at a depth of 3.1–6.9 m. Generalized linear models were developed to describe the relationship of shortnose sturgeon density and habitat variables. The model indicated that the shortnose sturgeon had significant preference to deeper areas within this region. The total abundance of shortnose sturgeon in the area was estimated to be 4836 ± 69 (mean ± standard error) using the ordinary kriging method to interpolate sturgeon density at unsampled sites. This overwintering habitat of shortnose sturgeon can be defined as critical habitat following the identification policies of the Canadian Species at Risk Act (SARA). Résumé : Nous avons étudié l’utilisation de l’habitat en hiver chez l’esturgeon à museau court (Acipenser brevirostrum) de janvier à mars 2005 dans le cours supérieur de la Kennebecasis, Nouveau-Brunswick, Canada, à l’aide d’un système nouveau de caméra vidéo et avec une approche de modélisation. Après un échantillonnage aléatoire, nous avons percé 187 trous dans la glace et énuméré et filmé 234 esturgeons. Les esturgeons se concentrent sur une surface de 2 ha au confluent des rivières Kennebecasis et Hammond sur un substrat plat et sablonneux à une profondeur de 3,1–6,9 m. Nous avons mis au point des modèles linéaires généralisés pour décrire la relation entre la densité des esturgeons à museau court et les variables de l’habitat. Le modèle indique que les esturgeons montrent une préférence significative pour les zones les plus profondes dans cette région. Nous estimons l’abondance totale des esturgeons à museau court dans la région à 4836 ± 69 (moyenne ± écart type) en utilisant la méthode ordinaire de krigage pour interpoler les densités de saumons aux sites non échantillonnés. Cet habitat d’hiver de l’esturgeon à museau court peut être désigné comme habitat essentiel d’après les critères d’identification de la loi canadienne sur les espèces en péril (LEP, « SARA »). [Traduit par la Rédaction]
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Introduction Sturgeons and paddlefishes are among the most endangered fishes in the world, with all 27 species listed on the International Union for Conservation of Nature and Natural Resources (IUCN) Red List: six species are critically endangered, 11 species are endangered, nine species are vulnerable, and one species is at low risk (IUCN 2006). Shortnose sturgeon (Acipenser brevirostrum) is one of the nine vulnerable species with a declining population trend (IUCN 2006). This trend has been attributed to blockage of spawning migrations by damming, regulation and dredging of rivers, bycatch
from harvest, and pollution (Kynard 1997; National Marine Fisheries Service (NMFS) 1998). It was listed as an endangered species in the United States in 1967 (US Fish and Wildlife Service 1999) and a species of special concern in Canada in 1980 by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC 2005). In spite of the urgent need of protection, there have only been a few studies on shortnose sturgeon habitat use and ecology. Shortnose sturgeon inhabit 19 rivers along the Atlantic coast of North America, from the Saint John River in New Brunswick, Canada, its only Canadian population, to the St. Johns River in Florida, USA (NMFS 1998). Since
Received 17 July 2006. Accepted 18 April 2007. Published on the NRC Research Press Web site at cjfas.nrc.ca on 1 September 2007. J19425 X.H. Li1 and M.K. Litvak.2 Department of Biology, University of New Brunswick, P.O. Box 5050, Saint John, NB E2L 4L5, Canada. J.E. Hughes Clarke. Department of Geodesy and Geomatics Engineering, University of New Brunswick, Fredericton, NB E3B 5A3, Canada. 1 2
Present address: Institute of Zoology, Chinese Academy of Sciences, Datun Road, Beijing 100101, China. Corresponding author (e-mail:
[email protected]).
Can. J. Fish. Aquat. Sci. 64: 1248–1257 (2007)
doi:10.1139/F07-093
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Dadswell’s (1979) systematic survey of the Saint John River population in the early to mid-1970s, only very basic information on habitat use of shortnose sturgeon has been studied in seven of these rivers (e.g., Kynard 1997; Kynard et al. 2000; Collins et al. 2002). In general, shortnose sturgeon are amphidromous, and their stay in salt water varies with latitude (Kynard 1997). Shortnose sturgeon are bottom feeders; they use their protractile mouths to suck up sand and mud to capture benthic crustaceans, molluscs, polychaetes, and small fishes (Dadswell 1979). Although we do know something of the summer habitat and activity, the overwintering habitat use of shortnose sturgeon is largely unknown. Dadswell (1979), based on his gill net sampling, suggested that there were seven discrete overwintering sites in the lower Saint John River occurring in deep areas of lakes and river channels or in halocline regions. Hall et al. (1991), using telemetry tracking, concluded that adult and juvenile use the freshwater–saltwater boundary region of the Savannah River during both fall and winter. Based on a telemetry survey and classification of several hierarchical classes of the habitat, Kynard et al. (2000) suggested that Connecticut River shortnose sturgeon increased their use of curves, channels (deep water), and sand substrate in the fall; winter habitat selection continued the fall pattern, but the fish were less mobile. However, the knowledge of the actual habitat utilization of shortnose sturgeon in winter is very limited. Clearly, locating the overwintering habitat and determining habitat preference of shortnose sturgeon is a priority for protecting this species. Thus, the objectives of our study were to locate the overwintering site, discover how shortnose sturgeon use their habitat in winter, and estimate their population size. To accomplish this goal, we developed an underwater video approach that involved calibrating fish density with regard to water turbidity, and this information was used to develop and compare spatial autocorrelation models and calculate shortnose sturgeon population size.
Materials and methods Study area and sonic telemetry We tagged three shortnose sturgeon in the fall of 2004 to help us determine a general location of the overwintering habitat. These fish were captured from the upper Kennebecasis River, a tributary of the Saint John River in New Brunswick, Canada, on 21 September 2004. They were each implanted with an ultrasonic transmitter (V16; VEMCO, Shad Bay, Nova Scotia, Canada) and released on that day. These coded transmitters emitted a sonic burst at random intervals of 80–100 s that were detected using both omnidirectional and directional hydrophones attached to a receiver – tag decoder (VR60; VEMCO). The omnidirectional hydrophone was used to detect if the tagged fish were within 800 m radius (maximum detection envelope) of the hydrophone. The directional hydrophone was used to determine the bearing of the fish relative to the location of the observer. Bearings were determined by using a compass aligned with the head of the directional hydrophone to establish the direction of the strongest sound received and decoded by the VEMCO VR60. Global positioning system (GPS) locations were obtained with a Magellan Meridian Marine WAAS (wide area augmentation system) enabled handset at four or five differ-
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ent observer locations (either from boat or shore) over a short period of time. This WAAS-capable receiver provided a position accuracy of better than 3 m 95% of the time (http://www.magellangps.com/en/). The actual fish locations, including 95% confidence interval ellipses, were calculated using the bearing and latitude–longitude of each observer location with the telemetry software Locate III (Nams 2004). We tracked these fish every other day in late September and October 2004 and found that they gradually moved upstream and stayed at one spot at the confluence of the Kennebecasis River and Hammond River for overwintering from 18 October 2004 (Fig. 1). Before good ice conditions, we occasionally tracked the sturgeon at the overwintering site during the winter by listening for the fish with the VEMCO VR60 at the river’s edge. No significant movement of shortnose sturgeon was detected during the winter, so we started the survey at the location of the tracked shortnose sturgeon when ice conditions permitted access to the site. Underwater video survey We used an underwater video camera (Atlantis™ underwater viewing system AUW-525C; Atlantis Cameras, Bergenfield, New Jersey) to observe the sturgeon, count the fish, and record the habitat variables at the overwintering site. Visual-based techniques have been used during fish survey for over 40 years. SCUBA divers can quantify fish populations by direct observation using standard visual belt transects (Brock 1954). Remote observation techniques, such as underwater video, have been used in a few aquatic biological studies, such as observing reactions of Atlantic salmon (Salmo salar) and whitefish (Coregonus lavaretus) to modified trap nets (Toivonen and Hudd 1993) and estimating gill net selectivity (Grant et al. 2004). Recently, sidescan sonar technology has been used to determine spatial distribution of lake sturgeon (Acipenser fulvescens) (Thomas and Hass 2002). This is an excellent approach but is limited in its ability to determine species identity of each sonar image, whereas video imaging allows identification to the species level. To our knowledge, no studies have used an underwater camera to observe sturgeon overwintering aggregation and habitat use. The survey was conducted from January to March 2005 when on-ice survey conditions were safe. We used a 10-inch ice auger (1 inch = 25.4 mm) (Jiffy Legend™ model 31; Jiffy Ice Drills, Sheboygan Falls, Wisconsin) to drill holes into the ice. The underwater video camera was attached to a 7 m long pole and was lowered through the holes in the ice to reach the river bottom. The camera orientation was parallel to the bottom so that we could have a side view and a greater radius of detection. The camera was turned 360 degrees to detect sturgeon within its zone of visibility. The images were recorded on a SONY DCR-HC30 digital video camera. The tapes were played back in the lab, and counts of shortnose sturgeon at each hole were recorded. Locations of the holes were randomly selected. GPS locations were obtained with a Magellan Meridian Marine handset. Depth at each hole was measured using the long pole. The substrate composition below each hole was visually classified following a classification system based on sediment terminology of the American Geophysical Union (Lane © 2007 NRC Canada
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Fig. 1. Study area of habitat use of shortnose sturgeon (Acipenser brevirostrum) in Kennebecasis River. The upper maps show the study area in New Brunswick, Canada. The lower map is the enlarged area of the solid rectangle in the upper map indicating the exact study location (rectangle) and the sonic tracking results from the three adult shortnose sturgeon (SNS) from 19 September 2004 to 16 April 2005.
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Table 1. The categories of substrate at the confluence of Kennebecasis River and Hammond River, New Brunswick, following classification of stream substrate materials by particle size (Lane 1947; Platts et al. 1983). Category
Size range (mm)
Index*
Silt Sand Fine gravel Coarse gravel Cobble–boulders
range; (iii) exponential model: semivariance = nugget + sill[1 – exp(–3lag/range)], when lag > 0; semivariance = 0, when lag = 0; and (iv) power model: semivariance = nugget + sill(lagrange). The actual semivariance model of sturgeon density between each hole was calculated using the SAS Variogram procedure (SAS Institute Inc., Cary, North Carolina). The model parameters were estimated as sill = 0.2, range = 10, and nugget = 0. The calculated semivariance, i.e., the experimental semivariance, was compared with the four theoretical semivariance models. The appropriate model was chosen based on the measurement of model fit that minimized the objective function: (2)
∑ [ semivariance(lag) − semivariance* (lag) ]2 lag
i.e., the residual sum of squares between the theoretical semivariance (indicated by asterisk) and experimental semivariance (Cressie 1993; Mello and Rose 2005). Using the theoretical variogram model with best fit, ordinary kriging predictions were computed as N
(3)
Z (V ) = ∑ λ i Z ( χ i ) i =1
where Z(V) is the estimate of density at an unsampled point, N is the number of holes, and λi is the weight attributed to sample xi (Mello and Rose 2005). The ordinary kriging was processed using ArcGIS software (ESRI, Redlands, California), and the output included predictions (sturgeon density) and standard error of the predictions. Habitat modeling A generalized linear model (GzLM) was developed to describe the habitat preference regarding associated habitat variables and has the following form (McCullogh and Nelder 1989): (4)
g(µ) = β 0 + β depth depth + β substrate substrate + β depth × substrate depth × substrate © 2007 NRC Canada
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Fig. 2. The density of shortnose sturgeon (Acipenser brevirostrum) at the confluence of Kennebecasis River and Hammond River, New Brunswick, Canada, from February to March 2005. The arrows indicate the downstream flow direction.
where µ = E(Y), Y is the density of shortnose sturgeon at each hole, depth and substrate are the covariates for observation Y, βdepth and βsubstrate are the linear coefficients, βdepth × substrate is the interaction coefficient, and g() is a logarithm link function that links the random component E(Y) to the systematic component β0 + βdepth depth + βsubstrate substrate + βdepth × substrate depth × substrate. The negative binomial distribution was used to describe the random component E(Y) (Power and Moser 1999).
Fig. 3. Frequency distribution of (a) count and (b) density of shortnose sturgeon (Acipenser brevirostrum) at the 187 holes drilled at the confluence of Kennebecasis River and Hammond River, New Brunswick, Canada, from February to March 2005. In (b), the 187 holes are given identity numbers (ID) from 1 to 187.
Results In total, 187 holes were drilled into the ice, 234 sturgeon were counted (Figs. 2 and 3) and their images were digitally recorded on video. The river bottom habitat within the study area was dominated by sandy substrate, mixed with gravel and silt substrate. At the confluence, the Kennebecasis and the Hammond rivers are 141–340 m and 68 m wide, respectively (Fig. 2). The depth is deeper (6–6.9 m) at the downstream section than the upstream section (3–4 m). The majority of the area is sandy, as 89.3% of the holes are over sandy substrate. The shortnose sturgeon concentrated at the deepest area on this sandy substrate. There is a deeper area with gravel or cobble substrate downstream of this area, but no fish were found there. No sturgeon were found on silt substrate, as all the sample plots with silt substrate were in shallow areas where depth was less then 2 m. Our survey indicated that shortnose sturgeon concentrated within a 2 ha area at the confluence between the Kennebecasis River and Hammond River (Fig. 2) on a flat sandy substrate at the depth of 3.1–6.9 m (Fig. 4). © 2007 NRC Canada
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Fig. 4. The density (count·m–2) of shortnose sturgeon (Acipenser brevirostrum) at each hole within the range of (a) depth and (b) substrate.
Table 2. Parameter estimates of the generalized linear model (GzLM) for shortnose sturgeon habitat use in the upper Kennebecasis River, New Brunswick, Canada. Parameter Model 1 Intercept Depth Substrate Depth × substrate Model 2 Intercept Depth
df
Estimate
SE
χ2
Pr > χ2
1 1 1 1
–5.9190 1.6942 0.8256 –0.4874
1.1746 0.4473 0.4949 0.2060
25.39 14.34 2.78 5.60
