The use of satellite tags to redefine movement patterns of spiny dogfish (Squalus acanthias) along the U.S. east coast: implications for fisheries management.

Amy E Carlson,Eric R Hoffmayer,Cindy A Tribuzio,James A Sulikowski,A Peter Klimley

doi:10.1371/journal.pone.0103384

Abstract

Spiny dogfish (Squalus acanthias) are assumed to be a highly migratory species, making habitual north-south migrations throughout their northwestern Atlantic United States (U.S.) range. Also assumed to be a benthic species, spiny dogfish stock structure is estimated through Northeast Fisheries Science Center (NEFSC) bottom-trawl surveys. Recent anomalies in population trends, including a recent four-fold increase in estimated spawning stock biomass, suggest alternative movement patterns could exist for this shark species. To obtain a better understanding of the horizontal and vertical movement dynamics of this species, Microwave Telemetry pop-up satellite archival X-Tags were attached to forty adult spiny dogfish at the northern (Gulf of Maine) and southern (North Carolina) extents of their core U.S. geographic range. Reconstructed geolocation tracks ranging in lengths from two to 12 months suggest that the seasonal migration patterns appear to be local in nature to each respective northern and southern deployment site, differing from previously published migration paradigms. Differences in distance and direction traveled between seasonal geolocations possibly indicate separate migratory patterns between groups. Kernel utilization distribution models also suggest strong separate core home ranges. Significant differences in seasonal temperature and depths between the two regions further substantiate the possibility of separate regional movement patterns between the two groups. Vertical utilization also suggests distinct diel patterns and that this species may not utilize the benthos as previously thought, potentially decreasing availability to benthic gear.

Highlights

Understanding both large and small scale movement patterns are essential components of successful fisheries management plans, especially for species that are considered highly migratory and/or are commercially harvested [1,2,3,4,5,6]
Given the uncertainties in stock estimates for this species and the potential vertical behavioral patterns that could possibly, limit the effective capture of spiny dogfish by Northeast Fisheries Science Center (NEFSC) bottom-trawl surveys, the goals of the current study were to: (1) deploy satellite tags on spiny dogfish at either extent of their core range (GOM and North Carolina (NC)), (2) determine whether migration patterns are in unison, synchronous and/or separate; (3) determine whether regional, seasonal, and diel differences exist in the vertical activity of the sharks between the two sample populations; and (4) compare the vertical and horizontal movement patterns of satellite tagged spiny dogfish to the NEFSC bottom-trawl survey over the same spatiotemporal period
The geolocation points used in the subsequent analysis all represent daily locations, the interval between points was variable between individuals depending on light levels collected by the tag

Summary

Introduction

Understanding both large (i.e. migratory) and small (i.e. diel) scale movement patterns are essential components of successful fisheries management plans, especially for species that are considered highly migratory and/or are commercially harvested [1,2,3,4,5,6]. They reveal only the net distance traveled and time elapsed between tagging and recovery location (see Kohler & Turner [10] for a review of shark studies) While this information has provided scientists with a wealth of knowledge concerning straight line movement patterns, the actual movement path of the fish, including the depths visited, remained unknown [5,6], [11]. The abundance and distribution of many marine fish species in United States (U.S.) coastal waters is measured by fisheries-independent surveys conducted by National Marine Fisheries Service (NMFS), various universities, and state agencies While these surveys have supplied critical datasets for ongoing stock assessments and management plans, they sample a large spatial scale, usually with a single gear type, and a restricted temporal scale (i.e. once or twice per year), only providing a limited spatial and temporal snapshot of the stock structure [12,13,14]

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Conclusion