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Quantification of Massive Seasonal Aggregations of Blacktip Sharks (Carcharhinus limbatus) in Southeast Florida.

Kajiura SM, Tellman SL - PLoS ONE (2016)

Bottom Line: This resulted in a maximum density of 803.2 sharks km(-2).Shark abundance was inversely correlated with water temperature and large numbers of sharks were found only when water temperatures were less than 25 °C.These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida, United States of America.

ABSTRACT
Southeast Florida witnesses an enormous seasonal influx of upper trophic level marine predators each year as massive aggregations of migrating blacktip sharks (Carcharhinus limbatus) overwinter in nearshore waters. The narrow shelf and close proximity of the Gulf Stream current to the Palm Beach County shoreline drive tens of thousands of sharks to the shallow, coastal environment. This natural bottleneck provides a unique opportunity to estimate relative abundance. Over a four year period from 2011-2014, an aerial survey was flown approximately biweekly along the length of Palm Beach County. A high definition video camera and digital still camera mounted out of the airplane window provided a continuous record of the belt transect which extended 200 m seaward from the shoreline between Boca Raton Inlet and Jupiter Inlet. The number of sharks within the survey transect was directly counted from the video. Shark abundance peaked in the winter (January-March) with a maximum in 2011 of 12,128 individuals counted within the 75.6 km(-2) belt transect. This resulted in a maximum density of 803.2 sharks km(-2). By the late spring (April-May), shark abundance had sharply declined to 1.1% of its peak, where it remained until spiking again in January of the following year. Shark abundance was inversely correlated with water temperature and large numbers of sharks were found only when water temperatures were less than 25 °C. Shark abundance was also correlated with day of the year but not with barometric pressure. Although shark abundance was not correlated with photoperiod, the departure of the sharks from southeast Florida occurred around the vernal equinox. The shark migration along the United States eastern seaboard corresponds spatially and temporally with the spawning aggregations of various baitfish species. These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase.

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Bathymetric map.Bathymetric map of the blacktip shark distribution range along the United States eastern seaboard. The broad shelf narrows dramatically in Palm Beach County, Florida (inset). Aerial survey flights were conducted between Boca Raton Inlet and Jupiter Inlet.
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pone.0150911.g002: Bathymetric map.Bathymetric map of the blacktip shark distribution range along the United States eastern seaboard. The broad shelf narrows dramatically in Palm Beach County, Florida (inset). Aerial survey flights were conducted between Boca Raton Inlet and Jupiter Inlet.

Mentions: This annual migration in the western Atlantic has been previously constructed from catch data [2, 16]. The blacktips overwinter in southeast Florida and begin their northward migration in March [2]. They are caught in large numbers off Daytona Beach, Florida in March and April [16] (Fig 2). Farther north, blacktips are abundant in Bulls Bay, South Carolina from May to September [16]. By May to June, the migration has reached North Carolina [2] and blacktips are rarely reported farther north [3]. However, tagging data indicate that they can be found as far north as Delaware Bay [17]. The sharks spend summer in the coastal waters off North Carolina, South Carolina, and Georgia before beginning their southward migration in September to October [2]. The blacktips again peak in abundance off Daytona Beach, Florida in September through November [16] and off Melbourne Beach, Florida in November and December [18].


Quantification of Massive Seasonal Aggregations of Blacktip Sharks (Carcharhinus limbatus) in Southeast Florida.

Kajiura SM, Tellman SL - PLoS ONE (2016)

Bathymetric map.Bathymetric map of the blacktip shark distribution range along the United States eastern seaboard. The broad shelf narrows dramatically in Palm Beach County, Florida (inset). Aerial survey flights were conducted between Boca Raton Inlet and Jupiter Inlet.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4814085&req=5

pone.0150911.g002: Bathymetric map.Bathymetric map of the blacktip shark distribution range along the United States eastern seaboard. The broad shelf narrows dramatically in Palm Beach County, Florida (inset). Aerial survey flights were conducted between Boca Raton Inlet and Jupiter Inlet.
Mentions: This annual migration in the western Atlantic has been previously constructed from catch data [2, 16]. The blacktips overwinter in southeast Florida and begin their northward migration in March [2]. They are caught in large numbers off Daytona Beach, Florida in March and April [16] (Fig 2). Farther north, blacktips are abundant in Bulls Bay, South Carolina from May to September [16]. By May to June, the migration has reached North Carolina [2] and blacktips are rarely reported farther north [3]. However, tagging data indicate that they can be found as far north as Delaware Bay [17]. The sharks spend summer in the coastal waters off North Carolina, South Carolina, and Georgia before beginning their southward migration in September to October [2]. The blacktips again peak in abundance off Daytona Beach, Florida in September through November [16] and off Melbourne Beach, Florida in November and December [18].

Bottom Line: This resulted in a maximum density of 803.2 sharks km(-2).Shark abundance was inversely correlated with water temperature and large numbers of sharks were found only when water temperatures were less than 25 °C.These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase.

View Article: PubMed Central - PubMed

Affiliation: Department of Biological Sciences, Florida Atlantic University, Boca Raton, Florida, United States of America.

ABSTRACT
Southeast Florida witnesses an enormous seasonal influx of upper trophic level marine predators each year as massive aggregations of migrating blacktip sharks (Carcharhinus limbatus) overwinter in nearshore waters. The narrow shelf and close proximity of the Gulf Stream current to the Palm Beach County shoreline drive tens of thousands of sharks to the shallow, coastal environment. This natural bottleneck provides a unique opportunity to estimate relative abundance. Over a four year period from 2011-2014, an aerial survey was flown approximately biweekly along the length of Palm Beach County. A high definition video camera and digital still camera mounted out of the airplane window provided a continuous record of the belt transect which extended 200 m seaward from the shoreline between Boca Raton Inlet and Jupiter Inlet. The number of sharks within the survey transect was directly counted from the video. Shark abundance peaked in the winter (January-March) with a maximum in 2011 of 12,128 individuals counted within the 75.6 km(-2) belt transect. This resulted in a maximum density of 803.2 sharks km(-2). By the late spring (April-May), shark abundance had sharply declined to 1.1% of its peak, where it remained until spiking again in January of the following year. Shark abundance was inversely correlated with water temperature and large numbers of sharks were found only when water temperatures were less than 25 °C. Shark abundance was also correlated with day of the year but not with barometric pressure. Although shark abundance was not correlated with photoperiod, the departure of the sharks from southeast Florida occurred around the vernal equinox. The shark migration along the United States eastern seaboard corresponds spatially and temporally with the spawning aggregations of various baitfish species. These baseline abundance data can be compared to future studies to determine if shark population size is changing and if sharks are restricting their southward migration as global water temperatures increase.

Show MeSH
Related in: MedlinePlus