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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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Spatial distribution of longline Catch Per Unit Effort (CPUE).In all panels, scaled circles indicate CPUE >0, crosses indicate CPUE  = 0. CPUE  =  sharks per 10 hook hours.
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pone-0016962-g002: Spatial distribution of longline Catch Per Unit Effort (CPUE).In all panels, scaled circles indicate CPUE >0, crosses indicate CPUE  = 0. CPUE  =  sharks per 10 hook hours.

Mentions: Between May and August 2009, longlines were set on 189 occasions, totaling 6,862 hook hours of soak time. A total of 221 sharks from 7 species were captured (Table 1). Although fishing was conducted throughout the entire atoll, the majority of effort was restricted to the northern half due to logistical limitations of operating from the Tern Island field station (Figs. 1, 2). The number of sets varied by month for both the deep lagoon and outside the barrier reef, due to weather restrictions on access to fishing locations. There was no significant difference in the number of monthly sets in the more protected and accessible shallow lagoon sites. The average duration of longline sets was longer in the shallow lagoon (6.2±2.7 h) than deep lagoon (4.0±0.8 h) and outer reef (4.0±1.2 h) sites. However, longer shallow lagoon sets were checked after approximately 4 h. There were no significant differences in CPUE between morning sets and afternoon sets for individual shark species or all species combined (P>0.05). Galapagos (36.2%), gray reef (Carcharhinus amblyrhynchos, 25.8%) and tiger (Galeocerdo cuvier, 20.4%) sharks were the numerically dominant species accounting for 82% of all sharks captured (Table 1). Sandbar (Carcharhinus plumbeus) and blacktip (Carcharhinus limbatus) sharks were captured less frequently, representing 10.4% and 4.1% of total shark catch respectively (Table 1). Species rarely encountered included scalloped hammerhead (Sphyrna lewini, N = 2, <1%) and whitetip reef sharks (Triaenodon obesus, N = 5, 2.3%) (Table 1).


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)

Spatial distribution of longline Catch Per Unit Effort (CPUE).In all panels, scaled circles indicate CPUE >0, crosses indicate CPUE  = 0. CPUE  =  sharks per 10 hook hours.
© Copyright Policy
Related In: Results  -  Collection

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

pone-0016962-g002: Spatial distribution of longline Catch Per Unit Effort (CPUE).In all panels, scaled circles indicate CPUE >0, crosses indicate CPUE  = 0. CPUE  =  sharks per 10 hook hours.
Mentions: Between May and August 2009, longlines were set on 189 occasions, totaling 6,862 hook hours of soak time. A total of 221 sharks from 7 species were captured (Table 1). Although fishing was conducted throughout the entire atoll, the majority of effort was restricted to the northern half due to logistical limitations of operating from the Tern Island field station (Figs. 1, 2). The number of sets varied by month for both the deep lagoon and outside the barrier reef, due to weather restrictions on access to fishing locations. There was no significant difference in the number of monthly sets in the more protected and accessible shallow lagoon sites. The average duration of longline sets was longer in the shallow lagoon (6.2±2.7 h) than deep lagoon (4.0±0.8 h) and outer reef (4.0±1.2 h) sites. However, longer shallow lagoon sets were checked after approximately 4 h. There were no significant differences in CPUE between morning sets and afternoon sets for individual shark species or all species combined (P>0.05). Galapagos (36.2%), gray reef (Carcharhinus amblyrhynchos, 25.8%) and tiger (Galeocerdo cuvier, 20.4%) sharks were the numerically dominant species accounting for 82% of all sharks captured (Table 1). Sandbar (Carcharhinus plumbeus) and blacktip (Carcharhinus limbatus) sharks were captured less frequently, representing 10.4% and 4.1% of total shark catch respectively (Table 1). Species rarely encountered included scalloped hammerhead (Sphyrna lewini, N = 2, <1%) and whitetip reef sharks (Triaenodon obesus, N = 5, 2.3%) (Table 1).

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