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The shark assemblage at French Frigate Shoals atoll, Hawai'i: species composition, abundance and habitat use.

Dale JJ, Stankus AM, Burns MS, Meyer CG - PLoS ONE (2011)

Bottom Line: Sharks were significantly less abundant in the shallow lagoon than adjacent habitats.The overall recapture rate was 5.4%.Additional data on long-term movements and habitat use of sharks at FFS are required to better assess the likely ecological impacts of shark culling.

View Article: PubMed Central - PubMed

Affiliation: Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Coconut Island, Kaneohe, Hawaii, United States of America. jjdale@hawaii.edu

ABSTRACT
Empirical data on the abundance and habitat preferences of coral reef top predators are needed to evaluate their ecological impacts and guide management decisions. We used longline surveys to quantify the shark assemblage at French Frigate Shoals (FFS) atoll from May to August 2009. Fishing effort consisted of 189 longline sets totaling 6,862 hook hours of soak time. A total of 221 sharks from 7 species were captured, among which Galapagos (Carcharhinus galapagensis, 36.2%), gray reef (Carcharhinus amblyrhynchos, 25.8%) and tiger (Galeocerdo cuvier, 20.4%) sharks were numerically dominant. A lack of blacktip reef sharks (Carcharhinus melanopterus) distinguished the FFS shark assemblage from those at many other atolls in the Indo-Pacific. Compared to prior underwater visual survey estimates, longline methods more accurately represented species abundance and composition for the majority of shark species. Sharks were significantly less abundant in the shallow lagoon than adjacent habitats. Recaptures of Galapagos sharks provided the first empirical estimate of population size for any Galapagos shark population. The overall recapture rate was 5.4%. Multiple closed population models were evaluated, with Chao M(h) ranking best in model performance and yielding a population estimate of 668 sharks with 95% confidence intervals ranging from 289-1720. Low shark abundance in the shallow lagoon habitats suggests removal of a small number of sharks from the immediate vicinity of lagoonal islets may reduce short-term predation on endangered monk seal (Monachus schauinslandi) pups, but considerable fishing effort would be required to catch even a small number of sharks. Additional data on long-term movements and habitat use of sharks at FFS are required to better assess the likely ecological impacts of shark culling.

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Mean Catch Per Unit Effort (CPUE) for shark species within habitats and overall.Shaded bars represent CPUE within habitats, unshaded bars represent overall CPUE. OB: Outside barrier reef; DL: Deep lagoon; SL: Shallow lagoon; CPUE  =  sharks per 10 hook hours.
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pone-0016962-g003: Mean Catch Per Unit Effort (CPUE) for shark species within habitats and overall.Shaded bars represent CPUE within habitats, unshaded bars represent overall CPUE. OB: Outside barrier reef; DL: Deep lagoon; SL: Shallow lagoon; CPUE  =  sharks per 10 hook hours.

Mentions: Overall CPUE (all sharks combined) varied significantly by habitat (Kruskal-Wallis, H = 11.0, P = 0.004) (Fig. 3). Within habitats, CPUE in shallow lagoon areas (mean CPUE  = 0.15±0.25) was significantly lower (P<0.01) than other locations, but there were no significant differences between deep lagoon areas (mean CPUE  = 0.39±0.35) and outside the barrier reef (mean CPUE  = 0.37±0.39). Galapagos, tiger and gray reef sharks were captured in all three habitats, whereas sandbar sharks were not captured in the shallow lagoon and blacktip sharks were not captured outside the barrier reef (Fig. 2, 3). Both of the scalloped hammerhead sharks were captured outside the barrier reef and 4 of 5 whitetip reef sharks were captured in the shallow lagoon. Of the three numerically dominant species, only catch rates of Galapagos sharks varied significantly among habitats (H = 7.13, P = 0.028). Catch per unit effort outside the barrier reef (mean CPUE  = 0.17±0.28) was significantly higher (P = 0.012) than shallow lagoon areas (mean CPUE  = 0.04±0.12), but there were no significant differences between deep (mean CPUE  = 0.10±0.19) and shallow lagoon, or between deep lagoon and outside the barrier reef.


The shark assemblage at French Frigate Shoals atoll, Hawai'i: species composition, abundance and habitat use.

Dale JJ, Stankus AM, Burns MS, Meyer CG - PLoS ONE (2011)

Mean Catch Per Unit Effort (CPUE) for shark species within habitats and overall.Shaded bars represent CPUE within habitats, unshaded bars represent overall CPUE. OB: Outside barrier reef; DL: Deep lagoon; SL: Shallow lagoon; CPUE  =  sharks per 10 hook hours.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3037392&req=5

pone-0016962-g003: Mean Catch Per Unit Effort (CPUE) for shark species within habitats and overall.Shaded bars represent CPUE within habitats, unshaded bars represent overall CPUE. OB: Outside barrier reef; DL: Deep lagoon; SL: Shallow lagoon; CPUE  =  sharks per 10 hook hours.
Mentions: Overall CPUE (all sharks combined) varied significantly by habitat (Kruskal-Wallis, H = 11.0, P = 0.004) (Fig. 3). Within habitats, CPUE in shallow lagoon areas (mean CPUE  = 0.15±0.25) was significantly lower (P<0.01) than other locations, but there were no significant differences between deep lagoon areas (mean CPUE  = 0.39±0.35) and outside the barrier reef (mean CPUE  = 0.37±0.39). Galapagos, tiger and gray reef sharks were captured in all three habitats, whereas sandbar sharks were not captured in the shallow lagoon and blacktip sharks were not captured outside the barrier reef (Fig. 2, 3). Both of the scalloped hammerhead sharks were captured outside the barrier reef and 4 of 5 whitetip reef sharks were captured in the shallow lagoon. Of the three numerically dominant species, only catch rates of Galapagos sharks varied significantly among habitats (H = 7.13, P = 0.028). Catch per unit effort outside the barrier reef (mean CPUE  = 0.17±0.28) was significantly higher (P = 0.012) than shallow lagoon areas (mean CPUE  = 0.04±0.12), but there were no significant differences between deep (mean CPUE  = 0.10±0.19) and shallow lagoon, or between deep lagoon and outside the barrier reef.

Bottom Line: Sharks were significantly less abundant in the shallow lagoon than adjacent habitats.The overall recapture rate was 5.4%.Additional data on long-term movements and habitat use of sharks at FFS are required to better assess the likely ecological impacts of shark culling.

View Article: PubMed Central - PubMed

Affiliation: Hawaii Institute of Marine Biology, University of Hawaii at Manoa, Coconut Island, Kaneohe, Hawaii, United States of America. jjdale@hawaii.edu

ABSTRACT
Empirical data on the abundance and habitat preferences of coral reef top predators are needed to evaluate their ecological impacts and guide management decisions. We used longline surveys to quantify the shark assemblage at French Frigate Shoals (FFS) atoll from May to August 2009. Fishing effort consisted of 189 longline sets totaling 6,862 hook hours of soak time. A total of 221 sharks from 7 species were captured, among which Galapagos (Carcharhinus galapagensis, 36.2%), gray reef (Carcharhinus amblyrhynchos, 25.8%) and tiger (Galeocerdo cuvier, 20.4%) sharks were numerically dominant. A lack of blacktip reef sharks (Carcharhinus melanopterus) distinguished the FFS shark assemblage from those at many other atolls in the Indo-Pacific. Compared to prior underwater visual survey estimates, longline methods more accurately represented species abundance and composition for the majority of shark species. Sharks were significantly less abundant in the shallow lagoon than adjacent habitats. Recaptures of Galapagos sharks provided the first empirical estimate of population size for any Galapagos shark population. The overall recapture rate was 5.4%. Multiple closed population models were evaluated, with Chao M(h) ranking best in model performance and yielding a population estimate of 668 sharks with 95% confidence intervals ranging from 289-1720. Low shark abundance in the shallow lagoon habitats suggests removal of a small number of sharks from the immediate vicinity of lagoonal islets may reduce short-term predation on endangered monk seal (Monachus schauinslandi) pups, but considerable fishing effort would be required to catch even a small number of sharks. Additional data on long-term movements and habitat use of sharks at FFS are required to better assess the likely ecological impacts of shark culling.

Show MeSH
Related in: MedlinePlus