Satellite tracking large numbers of individuals to infer population level dispersal and core areas for the protection of an endangered species

Abstract

Aim Tracking the dispersal patterns and habitat use of migratory species is necessary to delineate optimal areas for protection, with large sample sizes being more representative of the population. Here, we examine the dispersal patterns of a key Mediterranean loggerhead turtle (Caretta caretta) breeding population to identify priority foraging sites for protection.Location Zakynthos Island, Greece and the wider Mediterranean.Method We examined the dispersal patterns and foraging sites of 75 adult loggerheads (n = 38 males and 37 females) tracked from the breeding area of Zakynthos Island (Greece) from 2004 to 2011. We then combined our data with published sea turtle literature to identify key foraging sites for protection.Results While both males and females exhibited similar dispersal patterns, about 25% males remained < 100 km of Zakynthos, whereas all females (except one) migrated > 200 km. Integration of our data with the wider literature isolated 10 core sites in proximity to existing protected areas, which could potentially protect 64% of the Zakynthos population, while five sites support individuals from at least 10 other loggerhead breeding populations.Main conclusions Due to the widespread availability of neritic foraging grounds across the Mediterranean, sea turtles from Zakynthos exhibit disparate dispersal patterns. However, protecting only a few objectively defined important sites can encompass a large proportion of the foraging areas used and hence have considerable conservation benefit.

Movement patterns of marine turtles in the Mediterranean Sea: a review

“…In any case, PTTs will sooner or later detach from the carapace, although the gluing systems commonly employed guarantee quite long tag attachment durations, not uncommonly well over 1 year (e.g. Casale et al 2013a;Schofield et al 2013). PTTs can have an impact on turtle behaviour and energetics, especially during long movements, and carapace-attached tags have indeed been shown to increase the drag of marine turtles (Watson & Granger 1998;Jones et al 2013).…”

“…These findings confirmed the information obtained through recoveries of turtles tagged in western Greece (Margaritoulis et al 2003). Tracked Zakynthos turtles were distributed about roughly equally between these two foraging areas (Zbinden et al 2011;Schofield et al 2013), which indeed represent the largest neritic areas suitable for turtle foraging in the whole Mediterranean (Schofield et al 2013). Some of the turtles foraging in the northern Adriatic displayed seasonal migrations moving towards lower latitudes during the winter months (Zbinden et al 2011).…”

“…a direct and rather quick migration away from the breeding site to reach a specific feeding area, usually located in the neritic environment, where the turtle is then localised for months (type A pattern in Godley et al 2008). The most information is available for turtles belonging to the main rookery of Zakynthos Island, in western Greece (Table I), with a total of 36 females having been tracked so far (Zbinden et al 2008(Zbinden et al , 2011Schofield et al 2013). They have been shown to migrate towards two main destinations in the central Mediterranean (Figure 1), the Adriatic Sea (especially in its northern portion) and the continental shelf area offshore Tunisia and Libya (often, but rather improperly, indicated as the Gulf of Gabès, which actually only constitutes a small part of this area).…”

“…Females breeding in Cyprus displayed much the same type A movement pattern, migrating towards more disparate foraging areas along the North African shelf or the Syrian coast or even remaining in Cyprus Broderick et al 2007) (Figure 1). In both cases, it is not to be excluded that other foraging sites for these populations may be discovered in the future, given that the number of tracked females is still quite low with respect to the number of females breeding in these rookeries (Schofield et al 2013). Information on the migrations of turtles from the other Mediterranean rookeries is limited and mostly unpublished.…”

“…For males, the main difficulty lies in approaching the animals to tag them and deploy the satellite transmitters, since they very rarely leave the aquatic environment (e.g. Godley et al 2008;Arendt et al 2012a;Casale et al 2013a;Schofield et al 2013 and references therein). For juvenile turtles, the best available evidence on their spatial distribution has been obtained from genetic studies that have allowed the estimation of the contribution of different rookeries to the aggregations of juveniles frequenting a certain foraging area (e.g.…”