Growth and Survival of Hatchery-Produced Atlantic Sturgeon

Articles

Growth and Survival of Hatchery-Produced Atlantic Sturgeon Released as Young-of-Year into the Hudson River, New York Jerre W. Mohler,* John A. Sweka, Andrew Kahnle, Kathryn Hattala, Amanda Higgs, Mark DuFour, Matthew W. Breece, Dewayne A. Fox

J.W. Mohler, J.A. Sweka U.S. Fish and Wildlife Service, P.O. Box 75, Lamar, Pennsylvania 16848 A. Kahnle, K. Hattala, A. Higgs, M. DuFour New York State Department of Environmental Conservation, Hudson River Fisheries Unit, 21 South Putt Corners Road, New Paltz, New York 12561 Present address of M. DuFour: University of Toledo, Department of Environmental Sciences, Lake Erie Center, 6200 Bayshore Road, Oregon, Ohio 43613

M.W. Breece, D.A. Fox Delaware State University, 1200 N. DuPont Highway, Dover, Delaware 19901

Abstract In 2007, a team of U.S. scientists performed a status review of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus and concluded that the species would likely become endangered (U.S. Endangered Species Act 1973, as amended) in the foreseeable future over much of its range, including populations of the New York Bight, which is comprised of the Hudson and Delaware rivers. Therefore, we evaluated an experimental release of hatchery-produced Atlantic sturgeon that took place in 1994 to determine the value of using stocked fish as a population recovery tool. We obtained recapture data on hatchery fish (identified by presence of pelvic fin removal) from the Atlantic Coast Sturgeon Tagging Database. Our evaluation of retention for a pelvic fin removal mark on hatchery fish showed that 36% of clipped individuals retained a clean fin clip after 49 d. The minimum survival rate for hatchery fish to age 5 was estimated to be in the range of 0.49– 0.66% using documented recaptures (N = 24), known number of fish stocked, and results of the pelvic fin removal evaluation. Length and weight-at-age for recaptured hatchery fish at known ages 5–17 were within the range of values reported for wild fish whose ages were estimated by pectoral spine analysis. We also report that one ripe male hatchery fish at age 15 was captured along with other spermiating males at its parental spawning area in the Hudson River in 2009. Keywords: Atlantic; sturgeon; survival; hatchery; growth; Acipenser oxyrinchus oxyrinchus Received: January 14, 2011; Accepted: September 16, 2011; Published Online Early: December 2011; Published: June 2012 Citation: Mohler JW, Sweka JA, Kahnle A, Hattala K, Higgs A, DuFour M, Breece MW, Fox DA. 2012. Growth and survival of hatchery-produced Atlantic sturgeon released as young-of-year into the Hudson River, New York. Journal of Fish and Wildlife Management 3(1):23-32; e1944-687X. doi: 10.3996/012011-JFWM-005 Copyright: All material appearing in the Journal of Fish and Wildlife Management is in the public domain and may be reproduced or copied without permission unless specifically noted with the copyright symbol ß. Citation of the source, as given above, is requested. The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service. * Corresponding author: [email protected]

Introduction A major fishery for Atlantic sturgeon Acipenser oxyrinchus oxyrinchus began in the late 1800s when a caviar market was established. Record landings were Journal of Fish and Wildlife Management | www.fwspubs.org

reported in 1890, when over 3,350 metric tons of Atlantic sturgeon was landed from coastal rivers along the Atlantic Coast. The fishery collapsed in 1901 with less than 10% of the peak landings reported. Landings continued to decline to about 5% of the peak until June 2012 | Volume 3 | Issue 1 | 23

Growth and Survival of Hatchery-Produced Atlantic Sturgeon

1920 and are estimated to have remained between 1 and 5% since then (ASSRT 2007). A team of U.S. scientists performed a status review of Atlantic sturgeon and concluded that the species would likely become endangered in the foreseeable future over much of its range, including populations of the New York Bight, which is comprised of the Hudson and Delaware rivers (ASSRT 2007). By-catch mortality, water quality, lack of adequate state and/or Federal regulatory mechanisms, dredging activities, habitat impediment, and boat strikes were among the stressors identified as significant threats to the viability of Atlantic sturgeon populations. In order to provide information pertinent to recovery efforts for Atlantic sturgeon, we evaluated an experimental release of hatchery-produced Atlantic sturgeon that took place in 1994 to determine the value of using stocked fish as a population recovery tool. When using fish stocking as a management option for population recovery, the general goal of fishery managers is to build depleted or extirpated fish populations to self-sustaining levels. There has been considerable controversy over fish hatchery programs, with some stating that opportunistic stocking of Atlantic sturgeon without regard to protocols for maintenance of appropriate genetic diversity can contribute to population declines (St. Pierre 1999). Others believe that distribution of hatchery fish could result in outbreeding depression, loss of fitness, and negative impacts on wild fish production (Hilborn and Eggers 2000; Henderson et al. 2004; Jennings et al. 2010) and suggest that fish hatcheries have been used as a substitute for addressing root causes of declines in abundance (Waples 1999). Short-term evaluations of Atlantic sturgeon survival and growth are helpful but not conclusive in determining the value of using hatchery-produced fish to help achieve self-sustaining population goals due to the biology of the species. A major factor to be considered is that these fish generally display a long period of immaturity. With Atlantic sturgeon, the age to reach sexual maturity of females varies with latitude and ranges from 7 y in South Carolina rivers (Smith 1985) to 27 y in the St. Lawrence River, Canada (Scott and Scott 1988). On average, individuals from more southerly areas mature sooner (Gilbert 1989). Evaluating the contribution of hatchery Atlantic sturgeon to the target population requires a long-term project with the ability to discriminate hatchery fish from wild fish for a decade or more after stocking. The objectives of this paper are 1) to evaluate an experimental pelvic fin clip as an identifying mark for hatchery-produced fish and 2) to evaluate survival and growth of hatchery-produced Atlantic sturgeon using data reported to the Atlantic Sturgeon Coastal Tagging Database over a 17-y period and similar data reported for wild Atlantic sturgeon captured in the Hudson River.

Methods Producing, tagging, and stocking fish A female Atlantic sturgeon (2,200 mm total length; 67 kg) was captured via gill net on June 26, 1994, in the Journal of Fish and Wildlife Management | www.fwspubs.org

J.W. Mohler et al.

Hudson River at a well-documented spawning reach near Esopus Island at river kilometer (rkm) 135 in the vicinity of Hyde Park, New York. The female was transported to the U.S. Fish and Wildlife Service’s (USFWS’s) Northeast Fishery Center in Lamar, Pennsylvania, and given hormone injections of common carp pituitary extract according to techniques described in Conte et al. (1988) and Mohler (2004). Eggs were extracted and fertilized on June 30 using milt from two males that had been captured previously in the same river reach as the female. The milt was stored in a refrigerated, oxygenenriched environment and was composited just prior to fertilization. Offspring resulting from this spawning hatched on July 3 and were reared in indoor raceways and circular tanks using techniques described by Mohler (2004). Approximately 4,966 individuals were anesthetized on day 108 post-hatch (October 20, 1994) with 50 mg tricaine methane-sulfonate (MS-222) per liter of water, tagged with a coded wire tag (CWT; Northwest Marine Technologies, Shaw Island, WA) under the first dorsal scute, and the left pelvic fin was severed as close to the body as possible with surgical scissors. The fish were an average of 4.1 g (1.8–8.3 g) and 10.3 cm (7.8– 13.7 cm total length). The fish were maintained in indoor raceways and given a daily salt treatment of 1 ppt for 10 d. There were 39 mortalities during this 10-d period that were likely due to tagging and handling. On October 30, 1994, the survivors (N = 4,927) were transported from the Northeast Fishery Center at Lamar, Pennsylvania, to Newburgh, New York, and released in Newburgh Bay (rkm 90–99) of the Hudson River about 40 rkm downriver from where the parents had been captured (Figure 1). Temperature of the transport water was approximately 16uC and mean water temperature in Newburgh Bay was 15.5uC. Pelvic fin removal trial The method of pelvic fin removal was untested as a long-term identifying mark for Atlantic sturgeon, therefore a prestocking trial was performed on 120 fish produced from the same spawning episode described in the previous section. On day 67 post-hatch, 120 fish (average weight = 1.9 g) were randomly selected from the production lot and were anesthetized as already described. Pelvic fins were removed from 60 individuals by using surgical scissors to sever the fin as close as possible to the body. Sixty individuals were also used as controls and treated similarly with the exception of fin removal. For each treatment, equal numbers of fish (n = 20) were placed into three circular 54-L tanks and offered a closed formula dry diet (Fry Feed Kyowa, Type C-200, Biokyowa, Inc., Chesterfield, MO) at a rate of 4% initial tank biomass daily. About 50 g of noniodized salt was placed into each tank daily for a few days to promote fin healing. Tanks were maintained on flow-through conditions (flow rate not measured) at 17–19uC. An inventory for feed adjustment was performed after 19 d for all tanks, and feed rate was changed to 5% tank biomass daily. Final mortality, growth, and condition of the amputated area were recorded after 49 d for fish in each study treatment group. Growth of clipped vs. June 2012 | Volume 3 | Issue 1 | 24


J.W. Mohler et al.

Figure 1. Location of Atlantic sturgeon Acipenser oxyrinchus oxyrinchus broodstock capture (Esopus Island) and hatchery fingerling release (Newburg Bay) sites on the Hudson River, New York.

control sturgeon was then compared via t-tests using Sigma Stat Version 2.0 with an alpha level of 0.05. Evaluation of released sturgeon We evaluated growth and survival for stocked fish using data from both direct and indirect sampling sources. The first direct sampling took place beginning on May 31, 1995, approximately 6 mo after release of the hatchery fish and continued until December 15, 1995. Fish were captured using various-sized mesh gill nets via stratified random sampling at 57 locations distributed from the Tappan Zee Bridge (rkm 43) to Staatsburg, New York (rkm 194; Peterson et al., 2000). Another sampling study occurred from 1995 to 1997 through targeted gill netting in North Haverstraw Bay of the Hudson River (rkm 60–65) where previous acoustic tagging had been used to locate Atlantic sturgeon congregations (Cornell University 1998). Journal of Fish and Wildlife Management | www.fwspubs.org

Indirect sampling by researchers from various agencies ranging from New York to North Carolina also resulted in recapture of hatchery-released Atlantic sturgeon. Data documenting these recaptures were reported to the USFWS’s Maryland Fishery Resource Office that coordinates the Atlantic Sturgeon Coastal Tagging Database. We obtained length and weight data from the database for all fish reported from 1999 through 2011 (known ages = 5 through 17 years) with a missing left pelvic fin (Table 1). We considered hatchery-released fish to be age 1 on January 1, 1995. Since many researchers did not verify the presence of a CWT, we assumed all fish with missing left pelvic fins were of hatchery origin. Minimum survival rate to age 5 was calculated by the expression: Sm ~ðn=NÞ|100 June 2012 | Volume 3 | Issue 1 | 25


J.W. Mohler et al.

Table 1. Total lengths (TL; mm), fork lengths (FL; mm), weights (Wt; kg), capture date, age (y), and capture locations for recaptured hatchery Atlantic sturgeon Acipenser oxyrinchus oxyrinchus reported to the Atlantic Coast Sturgeon Tagging Database from 1999 to 2011. Repeat recaptures are not included. Database ID no.

TL (mm)

FL (mm)

Wt (kg)

Capture date

Age (y)

Capture location Long Island Sound, CT

352940001

857

725

2.8

September 18, 1999

5

352940190

920

795

4.8

August 18, 2000

6

Virginia Beach, VA

352940203

1,165

940

8.1

June 13, 2001

7

Delaware Bay, DE

352940204

1,060

910

8.4

September 7, 2001

7

Delaware Bay, DE

352940202

1,050

900

2.8

February 27, 2003

9

Pocomoke Sound, MD

352940196

1,240

1,060

8.7

November 8, 2005

11

Hudson River, NY

352940206

1,530

1,430

—

June 22, 2007

13

Long Island Sound, CT

352940207

1,620

1,590

—

June 28, 2007

13


352940208

1,760

1,570

23.8

July 17, 2007

13


352940209

1,550

1,430

21.1

August 7, 2007

13


352940210

1,290

1,140

11.6

June 27, 2008

14


352940211

1,195

1,040

11.3

July 9, 2008

14


352940212

1,830

1,620

33.8

July 10, 2008

14


352940213

1,540

1,360

19.6

July 17, 2008

14


352940218

1,950

1,730

45.0

June 17, 2009

15


352940057

1,873

—

45.5

June 17, 2009

15

Hudson River, NY

352940216

1,835

1,530

38.0

April 7, 2009

15

Bethany Beach, DE

352940219

1,925

1,730

—

July 15, 2009

15


352940220

1,085

940

7.4

July 15, 2009

15


352940221

1,980

1,770

43.0

April 20, 2011

17

Bethany Beach, DE

352940222

1,810

1,710

40.0

April 21, 2011

17

Bethany Beach, DE

352940223

1,820

1,620

36.0

May 2, 2011

17

Bethany Beach, DE

325940224

1,840

1,600

37.0

May 3, 2011

17

Bethany Beach, DE

325940226

1,890

1,640

37.0

May 9, 2011

17

Bethany Beach, DE

Where n is the number of Atlantic sturgeon that were reported to the Atlantic Sturgeon Coastal Tagging Database from 1999 to 2011 with a missing left pelvic fin and N is the number of fish released in 1994 (4,927). An alternative method for calculating minimum survival was also performed based on results from the pelvic fin removal trial that showed a proportion of fish had fully regenerated the clipped fin, rendering them visually unrecognizable as hatchery fish to researchers conducting indirect sampling. We calculated the alternative minimum survival rate using the expression: Sma ~fn=½N{Nðrf Þg|100 Where rf is the proportion of sturgeon in the fin removal trial which fully regenerated the clipped fin. We obtained length and weight data for wild Atlantic sturgeon from Dovel and Berggren (1983) and Van Eenennaam et al. (1996) in which sturgeon ages were determined via analysis of pectoral fin ray sections (i.e., pectoral spine analysis). Length and weight data for fish from all sources were log10 transformed and analysis of covariance was used to compare condition (weight at a given length). An alpha level of 0.05 was used in hypothesis testing. Due to imprecision in aging sturgeon by spine analysis (Rossiter et al. 1995; Paragamian and Beamesderfer 2003; Hurley et al. 2004), length and weight data were not compared statistically between Journal of Fish and Wildlife Management | www.fwspubs.org

wild and hatchery fish but simply plotted against age to construct a scatter plot.

Results Pelvic fin removal trial Post-clipping mortality over the first 19 d totaled only one Atlantic sturgeon from the clipped treatment and final mortality after 49 d was similar between clipped and control treatment at two and three individuals, respectively. Weights of clipped and control fish were similar (P = 0.541) after 49 d with mean weights (SD) at 19.6 (7.3) g and 18.8 (7.2) g. Mean lengths (SD) of clipped and control Atlantic sturgeon were also similar (P = 0.322) at 16.7 (2.6) cm and 16.2 (2.7) cm, respectively. Evaluation of the clipped fish after 49 d showed that 36.2% of the individuals had no sign of a left pelvic fin, 37.9% had partial fin regeneration, and 25.9% had fully regenerated pelvic fins. Recaptured hatchery sturgeon From 1995 to 1997, 110 stocked fish were recaptured through directed gill netting in Haverstraw Bay, Hudson River (Cornell University 1998). Hatchery fish comprised 35–53% of the total juvenile catch during that time period. Recaptured Atlantic sturgeon were reported to have slower growth, poorer condition, and higher rates of physical deformity than their wild counterparts. June 2012 | Volume 3 | Issue 1 | 26


J.W. Mohler et al.

Figure 2. Total length (TL)-weight (W) regression model using combined data on hatchery Atlantic sturgeon Acipenser oxyrinchus oxyrinchus from age 5 to 17 y reported in the Atlantic Coast Sturgeon Tagging Database and wild Atlantic sturgeon captured in the Hudson River, New York, of similar ages reported in Dovel and Berggren (1983) and Van Eenaennaam et al. (1996). W = (1.50 6 1029) 6 TL3.176.

Fifteen hatchery fish and 14 of their wild age-1 counterparts were captured during a 6.5-mo sampling period in 1995 at 15 locations in the Hudson River from the Tappan Zee bridge (rkm 43) to Staatsburg, New York (rkm 194). Both fin clips and CWTs were found on all hatchery fish captured, indicating minimal tag loss during the study (Peterson et al. 2000). Indirect sampling from 1999 to 2011 resulted in reports of 24 different Atlantic sturgeons with a missing left pelvic fin in the Atlantic Coast Sturgeon Tagging Database by numerous researchers from Long Island Sound to North Carolina waters (Table 1). One-half of the hatchery recaptures (12 of 24) were netted in Long Island Sound, but others were netted in Delaware Bay, coastal Delaware off Bethany Beach, the Hudson River, and coastal North Carolina (Table 1). In 1999 (age 5) there were still at least 24 individuals surviving out of the 4,927 fish originally stocked; therefore, we calculated the minimum survival to age 5 at 0.49% for the hatcheryorigin sturgeon. We calculated the alternative minimum survival (Sma) to age 5 at 0.66% using the expression previously described. Condition and growth comparisons There was no difference in condition (weight at a given length) among individuals reported by Dovel and Berggren (1983) and Van Eenaennaam et al. (1996) and the hatchery recaptures reported in the Atlantic Coast Sturgeon Tagging Database (P = 0.81). Therefore we combined data for a single weight-length regression line (W = [1.50 6 1029] 6 TL3.176; Figure 2). Though not compared statistically, we also found stocked fish lengthat-age and weight-at-age values were within the range of those reported for wild fish (Figure 3; Table 2). The Journal of Fish and Wildlife Management | www.fwspubs.org

raw data used in growth comparisons can be found in the Supplemental Material (Data S1, http://dx.doi.org/10. 3996/012011-JFWM-005.S1). It is important to note that we captured a spermiating male hatchery fish in 2009 at 15 y of age. This individual was captured along with wild spermiating males during spawning season (June 17) at a well-documented spawning area in the proximity of Esopus Island in the Hudson River (rkm 135). This was the same area where the parents of the hatchery fish were captured during the 1994 spawning season. The individual had a cleanly clipped area at the original location of the left pelvic fin and also tested positive for a CWT under the first dorsal scute confirming it was one of the hatchery fish released in 1994 (Figure 4).

Discussion The number of recaptures of hatchery fish was likely greater than actually reported in the Atlantic Coast Sturgeon Tagging Database considering results of the pelvic fin clip trial that showed only 36% of individuals exhibited a cleanly clipped fin location after 49 d. The pelvic fin clip served as an external identifier that was easily determined by Atlantic coastal researchers once they had been informed of its use. A fin clip mark must be used carefully and with full disclosure to the applicable research community to avoid removal of the same fin for different studies, thereby confounding study results. This is especially important for long-lived and highly migratory species such as Atlantic sturgeon. There are many other types of external tags available to sturgeon researchers, but due to the inherent retention longevity needed for a long-lived species such as sturgeon, we do not know of any commercially June 2012 | Volume 3 | Issue 1 | 27


J.W. Mohler et al.

Figure 3. Total length (a) and weight (b) at age 5 to 17 y for recaptured hatchery Atlantic sturgeon Acipenser oxyrinchus oxyrinchus reported in the Atlantic Coast Sturgeon Tagging Database and wild Atlantic sturgeon captured in the Hudson River, New York, of similar ages reported in Dovel and Berggren (1983) and Van Eenaennaam et al. (1996). Data were log10 transformed.

available external tags that will yield acceptable results. We found our secondary mark of CWTs in the hatchery fish to be inadequate for this type of study for two reasons: 1) handheld CWT detectors are expensive and not commonly used by sampling crews, and 2) due to the large amount of fish growth, the presence of the CWT is difficult to detect based on our observations with the 15-y-old hatchery recapture fish landed in 2009. Even though it represents only a single observation, the capture of a ripe hatchery male during spawning season along with other spermiating wild males at a known spawning area suggests that hatchery fish are capable of reproductive behavior similar to their wild counterparts. In addition, the capture of this particular fish shows that despite being reared for nearly 4 mo in a Journal of Fish and Wildlife Management | www.fwspubs.org

hatchery located in Lamar, Pennsylvania (Susquehanna River basin, Chesapeake Bay drainage), the individual was participating in a Hudson River spawning migration and returned to spawn where its parents had been captured 15 y prior. Cornell University (1998) found that stocked Atlantic sturgeon exhibited slower growth and poorer condition and had higher rates of physical deformity than their wild counterparts during their first 3 y of release, but we found overall growth of fish recaptured from 1999 to 2011 to be within the range of values reported for wild fish. This is similar to findings of Ireland et al. (2002) with white sturgeon Acipenser transmontanus for which growth rates and condition factors within 3 y after release were often poor but increased as hatchery fish adapted to natural conditions. June 2012 | Volume 3 | Issue 1 | 28


J.W. Mohler et al.

Table 2. Age (y), mean total lengths (TL; mm), weights (Wt; kg), range of measurements, and standard deviations (SD) for recaptured hatchery Atlantic sturgeon Acipenser oxyrinchus oxyrinchus as reported in the Atlantic Coast Sturgeon Tagging Database and wild Atlantic sturgeon captured in the Hudson River, New York from Dovel and Berggren (1983) and Van Eenaennaam et al. (1996). TL Age (y)

Mean

Wt

Range

SD

Mean

Range

SD

Van Eenennaam et al. (1996) N = 30a 5

—

—

—

3.4

3.0–4.1

0.6

6

1,270

1,244–1,295

21

5.0

4.8–5.0

0.1

7

1,270

1,219–1,320

46

4.7

4.6–4.8

0.1

8

1,245

1,219–1,295

27

—

—

—

9

1,298

1,219–1,520

98

—

—

—

10

1,410

1,219–1,651

160

—

—

—

11

1,568

1,244–1,800

175

—

—

—

12

1,680

1,320–1,960

188

30.8

27.2–35.8

4.5

13

1,767

1,327–2,057

167

30.7

26.8–39.0

2.7

14

1,785

1,560–2,057

121

33.7

27.2–39.9

4.5

15

1,871

1,651–2,057

102

33.5

28.1–38.6

5.1

16

1,804

1,727–1,880

77

37.0

36.3–37.7

0.7

17

1,803

1,727–1,880

62

36.8

33.1–38.6

2.6

Atlantic Coast Sturgeon Tagging Database (hatchery fish; 2011) N = 24b 5

857

857–857

0

2.8

2.8–2.8

—

6

920

920–920

0

4.8

4.8–4.8

—

7

1,113

1,060–1,165

74

8.2

8.0–8.3

0.2

8

—

—

—

—

—

—

9

1,050

1,050–1,050

2.8

2.8–2.8

—

10

—

—

—

—

—

—

11

1,208

1,175–1,240

46

9.4

8.7–10.1

1.0

12

—

—

—

—

—

—

13

1,615

1,530–1,760

104

22.5

21.1–23.8

1.9

14

1,463

1,195–1,830

284

18.9

11.3–33.8

11.0

15

1,912

1,873–1,950

54

42.3

45.0–45.5

0.4

16

—

—

—

—

—

—

17

1,868

1,810–1,980

62

38.6

36.0–43.0

2.6

0

a

Dovel and Berggren (1983) N = 21

a b

5

799

760–864

45

2.4

2.1–2.9

0.4

6

—

—

—

—

—

—

7

—

—

—

—

—

—

8

—

—

—

—

—

—

9

—

—

—

—

—

—

10

—

—

—

—

—

—

11

—

—

—

—

—

—

12

1,343

1,181–1,480

211

17.4

10.1–24.7

10.3

13

1,448

1,153–1,616

180

17.5

7.4–25.0

7.3

14

1,555

1,218–1,714

165

20.9

10.1–27.2

6.6

15

1,619

1,516–1,651

45

26.6

22.7–32.1

4.9

16

1,555

1,555–1,555

0

24.8

24.8–24.8

0.0

17

1,858

1,858–1,858

0

38.1

38.1–38.1

0.0

Wild Atlantic sturgeon. Recaptured hatchery Atlantic sturgeon.

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J.W. Mohler et al.

Figure 4. An Atlantic sturgeon Acipenser oxyrinchus oxyrinchus with a missing left pelvic fin captured on June 17, 2009, near Esopus Island in the Hudson River, New York. The individual tested positive for a coded-wire tag under the first dorsal scute confirming it was one of the fish released as a fingerling in 1994.

Dovel and Berggren (1983) and Van Eenennaam et al. (1996) used pectoral spine section analysis to estimate age for wild Atlantic sturgeon used in our study and the true ages were known for all hatchery recaptures. Accuracy and precision of age estimates for sturgeon is low (Rossiter et al. 1995; Paragamian and Beamesderfer 2003; Hurley et al. 2004); therefore, ages assigned to wild fish in our comparison are likely approximations. Using three independent readers, Van Eenennaam et al. (1996) estimated a potential error of 1 to 2 y for fish ranging in age from 15 to 30 y while aging for younger individuals was more accurate. Though ages for wild Atlantic sturgeon used in our analysis are considered approximations, they represent the best available data for comparison to the hatchery recaptures. Unless a captured individual was missing a left pelvic fin, it was not reported as a hatchery fish, but results showed that about 64% of the clipped individuals regenerated a clipped fin to some degree, and therefore even our alternative minimum survival rate to age 5 (0.66%) is likely conservative. In summary, we found that the minimum survival rate to age 5 for hatchery-produced Atlantic sturgeon Journal of Fish and Wildlife Management | www.fwspubs.org

was in the range of 0.49–0.66%. Recaptured hatchery Atlantic sturgeon also exhibited growth within ranges reported for wild Atlantic sturgeon. Even though only 36% of fish tested in the hatchery retained a clean pelvic fin clip, it proved to be a valuable external mark for identification of stocked Atlantic sturgeon and allowed us to make minimum survival calculations. We believe the results of our analysis show that the use of stocked Atlantic sturgeon can be a viable population recovery tool for future recovery programs for the species as long as recommended breeding and stocking protocols (ASMFC 2006) are followed as closely as possible.

Supplemental Material Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental material. Queries should be directed to the corresponding author for the article. Data S1. Total length (mm), weight (kg), and age of individual wild and hatchery-recaptured Atlantic sturgeons Acipenser oxyrinchus oxyrinchus. June 2012 | Volume 3 | Issue 1 | 30


Found at DOI: http://dx.doi.org/10.3996/012011JFWM-005.S1 (13 KB XLSX).

Acknowledgements The authors wish to thank all the researchers who willingly participated in reporting sturgeon captures to the Atlantic Coast Sturgeon Tagging Database from the following organizations: USFWS, Delaware Department of Natural Resources and Environmental Conservation, Division of Fish and Wildlife, New York Department of Environmental Conservation, Hudson River Fisheries Unit, and Delaware State University. We also especially thank Tom Savoy, Connecticut Department of Environmental Protection, Marine Fisheries Division, who captured and reported the majority of the pelvic fin–clipped sturgeon. Much gratitude goes to Sheila Eyler, USFWS for maintaining the Atlantic Coast Sturgeon Tagging Database, which continues to be a valuable tool for Atlantic sturgeon restoration efforts. Thank you to Joel Van Eenennaam, University of California at Davis, for providing individual sturgeon measurements used in this comparison. A debt of gratitude is also given to Mike Hendrix, former Director of the USFWS Northeast Fishery Center, Lamar, Pennsylvania, who took on the daunting task of positioning us to pioneer Atlantic sturgeon culture research that ultimately resulted in fingerlings available for this study. Many thanks also to Richard St. Pierre, retired USFWS biologist, who was very instrumental in coordinating with the State of New York to release the fingerling sturgeon in 1994. This manuscript was greatly improved by suggestions from the Subject Editor as well as those from Joseph E. Hightower and two anonymous reviewers. The use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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