Spatial distribution patterns of adult male Loggerhead sea turtles captured by research trawling in the Southeast US

​

Author: Mike Arendt

Affiliation: South Carolina Department of Natural Resources, Marine Resources Division

 

Pulled from SeaTurtle.org

In the past decade, a wealth of knowledge has emerged with respect to satellite telemetry documentation of the spatial distribution patterns for adult male sea turtles of several species. Regarding Loggerhead sea turtles (Caretta Caretta) in the northern hemisphere, adult males have been tracked following capture at breeding sites in both the NW Atlantic (Arendt et al. 2012a,b) and the Mediterranean Sea (Hays et al. 2010, Schofield et al. 2010) and on neritic foraging grounds off the coast of North Africa (Casale et al. 2013), West Africa (Varo-Cruz et al. 2013), and Japan (Sakamoto et al. 1997, Hatase et al. 2002).

​

Arendt et al. (2012) documented that 16 of 29 adult male Loggerhead sea turtles captured at the Port Canaveral, FL breeding aggregation subsequently emigrated to distant foraging grounds where they became localized in a variety of habitats ranging from shallow, near-shore coastal waters to deeper waters on the middle continental shelf.

 

Most migrant males moved north after breeding, and transit occurred between mid-May and late June. Because this transit coincides with the operational window of an important coastal trawl survey to assess the abundance, demographics, and health of sea turtles off SC, GA, and FL, we planned to use satellite telemetry with adult male Loggerhead sea turtles captured in this research survey, started in 2013, to answer the following questions:

​

1) Are adult male Loggerhead sea turtles captured in the trawl survey predominantly migrants or residents?

 

2) If migrant, do their foraging grounds overlap with those of adult male Loggerheads captured in Port Canaveral?

 

3) If resident, do their foraging grounds overlap with satellite tracks of juvenile Loggerhead sea turtles captured in the regional survey?

 

4) Do the over-wintering locations of adult male Loggerheads overlap with known over-wintering locations of adult females and juveniles that use the the same seasonal foraging grounds?

 

5) Do individual adult male Loggerheads use the same foraging grounds in subsequent years? 

 

To answer these questions, we began attaching satellite transmitters to adult male loggerhead sea turtles captured in the coastal trawl survey in 2013. To date one tag still remains at large after 290 days on the turtle. 

​

Some initial results:

​

1) With very few exceptions, adult male Loggerheads remained highly localized in the immediate vicinity where captured during the summer. Notable exceptions included a brief (20 days) egress loop exhibited by “Alan” off north Florida in 2013, and three males (“Fred”, “Jude”, “Evans”) captured in the Charleston SC shipping channel in May 2016 that emigrated north to the mid-Atlantic.

2) Among the three migrant males in 2016, all moved to similar areas occupied by migrant males captured in Port Canaveral in 2006 and 2007. Specifically, these three males in 2016 occupied shallow, near-shore waters off the Outer Banks of North Carolina as well as deeper, middle to outer continental shelf waters off VA and MD.

 

3) Detailed analysis of spatial distribution is pending, but cursory visual analysis suggests no difference in the summer foraging grounds of male Loggerheads captured in the coastal trawl survey compared to juvenile Loggerheads tagged with satellite transmitters during 2004-2007.

 

4) Despite tagging male Loggerheads after the mating season, over-wintering data was unfortunately only collected for six of 15 males. Two males (“Eastman”, “Mater’) over-wintered on the inner continental shelf in central to south Florida, while four others (“Jefe”, “Fuerte”, “Fred”, “Jude”) over-wintered on the middle to outer continental shelf between north Florida and southern North Carolina, but with maximum distance from shore independent of latitude.

5) A spring return to the general vicinity of where captured and tagged nine months earlier was documented for four males tagged prior to 2016. Two males tagged after capture in the Charleston, SC shipping channel in 2016 overwintered off NC, but as of mid-March 2017 it is still too early to determine if these males will return to where they were captured nine months earlier. One of these males (“Fred”) transmits intermittently, while the second (“Jude”) transmits regularly; thus, we are hopeful that we’ll be able to monitor at least one of these males during spring and into summer 2017.

​