Modeling loggerhead turtle movement in the Mediterranean: Importance of body size and oceanography

Adapting state–space models (SSMs) to telemetry data has been helpful for dealing with location error and for modeling animal movements. We used a combination of two hierarchical Bayesian SSMs to estimate movement pathways from Argos satellite‐tag data for 15 juvenile loggerhead turtles (Caretta caretta) in the western Mediterranean Sea, and to probabilistically assign locations to one of two behavioral movement types and relate those behaviors to environmental features. A Monte Carlo procedure helped propagate location uncertainty from the first SSM into the estimation of behavioral states and environment–behavior relationships in the second SSM. Turtles using oceanic habitats of the Balearic Sea (n = 9 turtles) within the western Mediterranean were more likely to exhibit “intensive search” behavior as might occur during foraging, but only larger turtles responded to variations in sea‐surface height. This suggests that they were better able than smaller turtles to cue on environmental features that concentrate prey resources or were more dependent on high‐quality feeding areas. These findings stress the importance of individual heterogeneity in the analysis of movement behavior and, taken in concert with descriptive studies of Pacific loggerheads, suggest that directed movements toward patchy ephemeral resources may be a general property of larger juvenile loggerheads in different populations. We discovered size‐based variation in loggerhead distribution and documented use of the western Mediterranean Sea by turtles larger than previously thought to occur there. With one exception, only individuals >57 cm curved carapace length used the most westerly basin in the Mediterranean (western Alborán Sea). These observations shed new light on loggerhead migration phenology

Supplement 1. WinBUGS code, and sample data and initial values, for stage-2 state–space model analysis of movement paths.

<h2>File List</h2><blockquote> <p><a href="CodeSupplement_model.txt">CodeSupplement_model.txt</a> -- WinBUGS code</p> <p><a href="CodeSupplement_data and inits.txt">CodeSupplement_data and inits.txt</a> -- sample data and initial values</p> </blockquote><h2>Description</h2><blockquote> <p>“CodeSupplement_model.txt” contains WinBUGS code for running the stage-2 state-space model <i>in</i>: S. Eckert, J. Moore, D. Dunn, R. Sagarminaga, K. Eckert, P. Halpin "Hierarchical state-space models of loggerhead sea turtle (<i>Caretta</i> <i>caretta</i>) movement in relation to turtle size and oceanographic features in the western Mediterranean Sea". Code includes prior specification for all estimated parameters and hyper-parameters (stochastic nodes), including parameters describing covariate effects on behavioral switch probabilities and parameters describing movement characteristics (rates and variance of turn angles) for two behavioral states. Code includes normal and wrapped Cauchy likelihoods for mode-specific movement parameters and a Bernoulli likelihood for behavioral state. Model is based on a hierarchical switch model <i>from</i>: J. Morales, D. Haydon, J. Frair, K. Holsinger, and J. Fryxell. Extracting more out of reloction data: building movement models as mixtures of random walks. Ecology 85:2436–2445.</p> <p>“CodeSupplement_data and inits.txt” contains sample data and initial values in WinBUGS format. All data were standardized as <i>z</i>-scores for analysis.</p> </blockquote

Working Group on Bycatch of Protected Species (WGBYC)

WGBYC planned to address seven Terms of Reference, one of which was a special request from the European Commission on emergency bycatch mitigation measures for common dolphin in the Bay of Biscay and harbour porpoise in the Baltic Sea (ToR G). ToR G demanded a great deal of resources from WGBYC and, coupled with the COVID–19 disruption where WGBYC work had to be carried out remotely, this meant it was not possible to complete all tasks. The 2020 report is structured in the same order as the ToRs. Note that ToR E was not addressed while ToR G is reported in WKEMBYC (2020). All data submissions were requested via a formal WGBYC/ICES data call (Annex 6: below). The data call requested data on fishing effort, monitoring effort and PETS (protected, endangered, and threatened species of marine mammals, seabirds, reptiles, and fish) bycatch incidents in 2018. 19 of the 24 countries that contacted (18 ICES countries and 6 Mediterranean non-ICES countries) responded. WGBYC did not accept data brought to the meeting, but where problems were found during assessments with country submissions, updated versions were accepted. The quality and scope of Member States (MS) reports on the implementation of Regulation 812/2004 (cetacean bycatch) during 2018 remain varied (ToR A). Most countries have relied on monitoring through their DCF sampling programmes rather than implementing dedicated ob-server programmes. This means that métiers that pose the greatest risk of cetacean bycatch are generally under-sampled and bycatch is underestimated. Regulation 812/2004 was repealed and replaced in June 2019 by the Technical Conservation Measures Regulation (Regulation (EU) 2019/1241) and PETS bycatch monitoring is further implemented through the EU-MAP (Regula-tion (EU) 2017/1004). For 2018, data received through the WGBYC data call amounted to 82 cetaceans (5 species); 175 seals (4 species), 696 birds (at least 22 species); 37 644 elasmobranchs (at least 49 species); 2061 teleost fish (9 species) and 134 turtles (at least 2 species). Equivalent data from non-EU countries was also received from the USA and Iceland. Bycatch of marine mammals was observed in all ecoregions and several gears including gillnets, traps, longlines, and trawls. Seabirds were by-caught in most ecoregions, mainly in nets and longlines. In 2018, bycaught marine turtles were recorded mostly in set nets and trawls in the Mediterranean and in longlines in the Azores. High bycatch rates were observed for some elasmobranch species which are of conservation concern, particularly in trawl gears in the Celtic Sea, the Greater North Sea and Western Mediterranean, and nets in the Celtic Sea. In the US Northwest Atlantic, the gear of most concern are set nets for marine mammals and sea turtles. The gears of most concern in Iceland are set nets (birds and marine mammals) and longlines (birds). Eight countries also contributed numbers of bycaught stranded cetaceans. Bycatch was the predominant cause of death of common dolphins stranded in the Bay of Biscay and Channel. Member states compliance with the ‘pinger’ requirements of Regulation 812/2004 is difficult to gauge from the submitted reports due to reporting inconsistencies and incomplete information (ToR B). Only the United Kingdom appears to comply fully, reporting that all relevant vessels are equipped with “DDD” pingers used under a derogation and there is active enforcement in place. But in general, there has been little progress in the mitigation of cetacean bycatch and the effectiveness of pingers appears to vary among fishing métiers and geographical areas. WGBYC continues to have insufficient data to examine bycatch rates according to pinger use within their database