71 research outputs found
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Recovery of critically endangered Nassau grouper (Epinephelus striatus) in the Cayman Islands following targeted conservation actions.
Many large-bodied marine fishes that form spawning aggregations, such as the Nassau grouper (Epinephelus striatus), have suffered regional overfishing due to exploitation during spawning. In response, marine resource managers in many locations have established marine protected areas or seasonal closures to recover these overfished stocks. The challenge in assessing management effectiveness lies largely in the development of accurate estimates to track stock size through time. For the past 15 y, the Cayman Islands government has taken a series of management actions aimed at recovering collapsed stocks of Nassau grouper. Importantly, the government also partnered with academic and nonprofit organizations to establish a research and monitoring program (Grouper Moon) aimed at documenting the impacts of conservation action. Here, we develop an integrated population model of 2 Cayman Nassau grouper stocks based on both diver-collected mark-resight observations and video censuses. Using both data types across multiple years, we fit parameters for a state-space model for population growth. We show that over the last 15 y the Nassau grouper population on Little Cayman has more than tripled in response to conservation efforts. Census data from Cayman Brac, while more sparse, show a similar pattern. These findings demonstrate that spatial and seasonal closures aimed at rebuilding aggregation-based fisheries can foster conservation success
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The effects of semi-chronic thermal stress on physiological indicators in steelhead Oncorhynchus mykiss
The physiological response of juvenile steelhead (Oncorhynchus mykiss) to prolonged heat stress was examined by exposing replicated groups of fish to 25 consecutive days at 15°C, 23°C, and 25°C followed by a 55 day recovery period at 15°C. We found that at temperatures ≥25°C, steelhead consumed significantly less food per day and had elevated feed conversion rates but experienced slower growth, reduced body size, lower body fat, and elevated heat shock protein 70 (hsp 70) levels relative to fish 2°C and 10°C cooler. Growth decreased 24.4% and 27.1% for length and mass, respectively, between 15°C and 23°C, and an additional 60% and 56.5% between 23°C and 25°C during exposures. While growth increments and lipid levels recovered to control levels after water temperature was reduced, body size of the 25°C exposed fish lagged throughout the experiment. Our results indicate a temperature threshold after which steelhead exposed to semi-chronic thermal stress incur a physiological debt. Heat shock protein 70 levels were detectable up to 25 days post-stress in fin and liver tissues, providing evidence that this is a useful metric for thermal stress that can be assessed non-lethally, an important technique relevant for monitoring thermal-habitat restoration efforts for threatened and endangered salmonids.Keywords: Age and Growth, Physiology, Water Qualit
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A cross-shelf gradient in δ¹⁵N stable isotope values of krill and pollock indicates seabird foraging patterns in the Bering Sea
Concurrent measurements of predator and prey δ¹⁵N isotope values demonstrated that a cross-shelf
isotopic gradient can propagate through a marine food web from forage species to top-tier predators and
indicate foraging areas at a scale of tens of kilometers. We measured δ¹³C and δ¹⁵N in muscle tissues of
thick-billed murres (Uria lomvia) and black-legged kittiwakes (Rissa tridactyla), and in whole body tissues
of walleye pollock (Gadus chalcogrammus) and krill (Thysanoessa spp), sampled across the continental
shelf break in the Bering Sea in 2008 and in 2009. We found significant basin-shelf differences at fine
scales (<100 km) in δ¹⁵N among murres but not kittiwakes, and no such differences in δ¹³C in either
seabird species at that scale. We then quantified the multi-trophic signal and spatial structure of a basin-shelf
δ¹⁵Nitrogen gradient in the central and southern Bering Sea, and used it to contrast foraging
patterns of thick-billed murres and kittiwakes on the open ocean. Seabird muscle δ¹⁵N values were
compared to baselines created from measurements in krill and pollock tissues sampled concurrently
throughout the study area. Krill, pollock, and murre tissues from northern, shallow, shelf habitat
(200 m) to the
south and west. Krill δ¹⁵N baseline values predicted 35–42% of the variability in murre tissue values.
Patterns between kittiwakes and prey were less coherent. The persistence of strong spatial autocorrelation
among sample values, and a congruence of geospatial patterns in δ¹⁵N among murre and prey
tissues, suggest that murres forage repeatedly in specific areas. Murre isotope values showed distinct
geospatial stratification, coincident with the spatial distribution of three colonies: St. Paul, St. George,
and Bogoslof. This suggests some degree of foraging habitat partitioning among colonies.Keywords: Isotopes,
Rissa tridactyla,
Food web,
Shelf edge,
Habitat partitioning,
Kittiwake,
Murre,
Uria lomvi
Migratory behavior of aggregating male Tiger Grouper (Mycteroperca tigris) in Little Cayman, Cayman Islands
Tiger Grouper (Mycteroperca tigris) form fish spawning aggregations (FSAs) around the winter full moons (typically January through April) in the Caribbean. Males defend territories to attract mates in a lek-like reproductive strategy. Prior studies have documented rapid declines in populations with FSA-associated fisheries. This study examines the migratory behavior of adult male Tiger Grouper in Little Cayman, Cayman Islands, to better understand the impacts of aggregation fishing. As part of the Grouper Moon Project, we acoustically tagged ten spawning male Tiger Grouper at the western end of Little Cayman in February 2015. Using a hydrophone array surrounding the island, we tracked the movements of the tagged fish for 13 months. We observed 3 migratory strategies: resident fish (n = 2) that live at the FSA site, neighboring fish (n = 5) that live within 4 km of the site, and commuter fish (n = 3) that travel over 4 km for spawning. Fish began aggregating 2 days before the full moon and left 10–12 days after the full moon, from January to May. Regardless of migratory strategy, all tagged fish that aggregated after February 2015 returned to the west end FSA. However, in January 2016, one fish appeared to attend a different FSA closer to its presumed home territory. Tiger Grouper may establish multiple FSAs around Little Cayman, and males appear to attend FSAs near their home territories. Protracted spawning seasons, FSA site infidelity, and putative FSA catchments should all be considered to ensure sustainable fisheries management for this important species.publishedVersio
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Hepatic heat shock protein 70 and plasma cortisol levels in rainbow trout after tagging with a passive integrated transponder
This study examined the potentially stressful
effects of tagging juvenile rainbow trout Oncorhynchus mykiss
with passive integrated transponder (PIT) tags by measuring
short-term (<120-h) changes in plasma concentrations of
cortisol and hepatic heat shock protein 70 (hsp70). In a
laboratory experiment, plasma cortisol levels were measured
in fish before they were tagged (0 h) and at 2, 6, 24, and 120 h
after being tagged. Hepatic hsp70 levels were measured at 0,
24, and 120 h. All results were compared with those for fish
that were handled but not tagged. Plasma cortisol levels were
significantly higher in both treatment groups (tagged and
handled but not tagged) at 2 h than in the pretreatment groups
(0 h). Plasma cortisol levels in the treatment groups returned to
near pretreatment levels by 6 h. However, there was a
significant difference in plasma cortisol levels between
treatment groups at 6 h. There were no significant differences
in hepatic hsp70 levels among the two treatment groups, and
hepatic hsp70 levels did not change through time. Our results
suggest that PIT tagging is a low-impact tagging procedure for
juvenile salmonids.Keywords: Rainbow trout, passive integrated transponders, plasma cortiso
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Enzyme-Linked Immunosorbent Assay (ELISA) of Vitellogenin in Temperate Basses (Genus Morone): Plasma and In Vitro Analyses
Blood levels of the egg yolk precursor vi-
tellogenin (VTG) can be used as a definitive marker for
the onset and progress of maturation in female teleosts.
In the present study, an enzyme-linked immunosorbent
assay (ELISA) was developed to measure VTG in blood
plasma from three species of temperate basses. The an-
tigen capture, competitive ELISA is based on a rabbit
antiserum raised against striped bass Morone saxatilis
VTG and uses purified striped bass VTG as standard and
in the final antigen capture step. The assay was validated
for detecting VTG in the plasma of maturing female
striped bass, white perch M. americana, and white bass
M. chrysops. Serial dilutions of blood plasma from vi-
tellogenic females of all three species yielded VTG
curves that paralleled the standard curve in the ELISA,
whereas no cross reactivity was observed for plasma
obtained from males of any Morone species. The work-
ing range of the ELISA was 33–1,118 ng/mL (90–10%
of binding), and the intra- and interassay coefficients of
variation (100 3 SD/mean) at 50% binding were 3.8%
(N 5 20) and 5.94% (N 5 4), respectively. Complete
recovery (detection) in the ELISA was verified for a
known quantity of VTG added to male striped bass plas-
ma. Changes in plasma VTG concentrations during the
annual reproductive cycle of female striped bass were
measured both by ELISA and an established radial im-
munodiffusion assay (RIDA) based on the same anti-
serum and standard. Vitellogenin was detected in ma-
turing females 7–8 months prior to spawning and the
correlation between individual VTG values measured by
ELISA and the RIDA was very high (r2 5 0.95). The
highly sensitive and precise VTG ELISA should allow
aquaculture and fisheries biologists to evaluate the gen-
der and maturational status of individual fish of any
Morone species during most of the year. Finally, VTG
was detected by ELISA in incubation medium following
culture of white perch liver fragments with 1 3 1026 M
estradiol-17b, providing the basis for an in vitro method
to study the physiology and toxicology of vitellogenesis
in temperate basses.Keywords: vitellogenin, ELISA, temperate basses, enzyme-linked immunosorbent assa
Protected fish spawning aggregations as self-replenishing reservoirs for regional recovery
Dispersal of eggs and larvae from spawning sites is critical to the population dynamics and conservation of marine fishes. For overfished species like critically endangered Nassau grouper (Epinephelus striatus), recovery depends on the fate of eggs spawned at the few remaining aggregation sites. Biophysical models can predict larval dispersal, yet these rely on assumed values of key parameters, such as diffusion and mortality rates, which have historically been difficult or impossible to estimate. We used in situ imaging to record three-dimensional positions of individual eggs and larvae in proximity to oceanographic drifters released into egg plumes from the largest known Nassau grouper spawning aggregation. We then estimated a diffusion–mortality model and applied it to previous years' drifter tracks to evaluate the possibility of retention versus export to nearby sites within 5 days of spawning. Results indicate that larvae were retained locally in 2011 and 2017, with 2011 recruitment being a substantial driver of population recovery on Little Cayman. Export to a nearby island with a depleted population occurred in 2016. After two decades of protection, the population appears to be self-replenishing but also capable of seeding recruitment in the region, supporting calls to incorporate spawning aggregation protections into fisheries management.publishedVersio
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Patterns of color phase indicate spawn timing at a Nassau grouper Epinephelus striatus spawning aggregation
Nassau grouper Epinephelus striatus are a large bodied, top level predator that is ecologically important throughout
the Caribbean. Although typically solitary, Nassau grouper form large annual spawning aggregations at predictable times in specific
locations. In 2003, The Cayman Islands Marine Conservation Board established protection for a newly rediscovered Nassau
grouper spawning aggregation on Little Cayman, British West Indies. The large size of this aggregation provides a unique opportunity
to study the behavior of Nassau grouper on a relatively intact spawning aggregation. During non-spawning periods Nassau
grouper display a reddish-brown-and-white barred coloration. However, while aggregating they exhibit three additional color
phases: “bicolor”, “dark”, and “white belly”. We video sampled the population on multiple days leading up to spawning across
five spawning years. Divers focused a laser caliper equipped video camera on individual fish at the aggregation. We later analyzed
the video to determine the length of the fish and record the color phase. Our observations show that the relative proportion
of fish in the bicolor color phase increases significantly on the day leading up to the primary night of spawning. The increase in
the proportion of the bicolor color phase from 0.05 early in the aggregation to 0.40 on the day of spawning suggests that this color
phase conveys that a fish is behaviorally and physiologically prepared to spawn. Additionally, 82.7% of fish exhibiting dark or
white belly coloration early in the aggregation period suggests that these color phases are not only shown by female fish as was
previously posited [Current Zoology 58 (1): 73–83, 2012].This is the publisher’s final pdf. The published article is copyrighted by Current Zoology, Institute of Zoology, Chinese Academy of Sciences and can be found at: http://www.actazool.org/.Keywords: Nassau grouper, Epinephelus striatus, Nuptial coloration, Spawning aggregation, Spawning behavio
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Paenibacillus thiaminolyticus is not the cause of thiamine deficiency impeding lake trout (Salvelinus namaycush) recruitment in the Great Lakes
Thiamine (vitamin B₁) deficiency is a global concern affecting wildlife, livestock, and humans. In Great Lakes salmonines, thiamine deficiency causes embryo mortality and is an impediment to restoration of native lake trout (Salvelinus namaycush) stocks. Thiamine deficiency in fish may result from a diet of prey with high levels of thiaminase I. The discoveries that the bacterial species Paenibacillus thiaminolyticus produces thiaminase I, is found in viscera of thiaminase-containing prey fish, and causes mortality when fed to lake trout in the laboratory provided circumstantial evidence implicating P. thiaminolyticus. This study quantified the contribution of P. thiaminolyticus to the total thiaminase I activity in multiple trophic levels of Great Lakes food webs. Unexpectedly, no relationship between thiaminase activity and either the amount of P. thiaminolyticus thiaminase I protein or the abundance of P. thiaminolyticus cells was found. These results demonstrate that P. thiaminolyticus is not the primary source of thiaminase activity affecting Great Lakes salmonines and calls into question the long-standing assumption that P. thiaminolyticus is the source of thiaminase in other wild and domestic animals
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Prey Patch Patterns Predict Habitat Use by Top Marine Predators with Diverse Foraging Strategies
Spatial coherence between predators and prey has rarely been observed in pelagic marine ecosystems. We used measures of the environment, prey abundance, prey quality, and prey distribution to explain the observed distributions of three co-occurring predator species breeding on islands in the southeastern Bering Sea: black-legged kittiwakes (Rissa tridactyla), thick-billed murres (Uria lomvia), and northern fur seals (Callorhinus ursinus). Predictions of statistical models were tested using movement patterns obtained from satellite-tracked individual animals. With the most commonly used measures to quantify prey distributions - areal biomass, density, and numerical abundance - we were unable to find a spatial relationship between predators and their prey. We instead found that habitat use by all three predators was predicted most strongly by prey patch characteristics such as depth and local density within spatial aggregations. Additional prey patch characteristics and physical habitat also contributed significantly to characterizing predator patterns. Our results indicate that the small-scale prey patch characteristics are critical to how predators perceive the quality of their food supply and the mechanisms they use to exploit it, regardless of time of day, sampling year, or source colony. The three focal predator species had different constraints and employed different foraging strategies - a shallow diver that makes trips of moderate distance (kittiwakes), a deep diver that makes trip of short distances (murres), and a deep diver that makes extensive trips (fur seals). However, all three were similarly linked by patchiness of prey rather than by the distribution of overall biomass. This supports the hypothesis that patchiness may be critical for understanding predator-prey relationships in pelagic marine systems more generally
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