Abstract
AbstractBluefin Tuna Thunnus thynnus are highly sought after in commercial and recreational fisheries along the East Coast of North America. To appropriately assess and manage Atlantic Bluefin Tuna (ABT), it is necessary to understand their habitat use during multiple ontogenetic stages. We tagged 17 juvenile ABT in the northwest Atlantic Ocean with pop-up satellite archival tags (PSATs) to determine environmental factors that may affect habitat use. The PSATs were deployed off the coast of Massachusetts in August and September 2012. A generalized linear mixed model was applied to determine factors affecting the mean depth occupied by fish, and beta regression was used to understand factors affecting the proportion of time spent below the thermocline. Thermocline depth significantly affected the mean depth occupied by juvenile ABT and the proportion of time they spent below the thermocline. Time period (dawn, day, dusk, and night) also significantly affected the mean depth occupied by juvenile ABT. Additi...
Highlights
Thermocline depth significantly affected the mean depth occupied by juvenile Atlantic Bluefin Tuna (ABT) and the proportion of time they spent below the thermocline
We examined the following null hypotheses: (1) environmental factors do not affect the mean depth occupied by juvenile ABT and (2) environmental factors do not affect the proportion of time juvenile ABT spend in waters below the thermocline
Analyses.—We used the data from each pop-up satellite archival tags (PSATs) to (1) model the mean depth occupied by juvenile ABT and the proportion of time they spent below the thermocline and (2) explore the effects
Summary
Habitat use by adult ABT is well studied (Lutcavage et al 2000; Block et al 2001; Newlands et al 2004; Schick et al 2004; Stokesbury et al 2004; Wilson et al 2005; Teo et al 2007; Walli et al 2009; Druon et al 2016), less information is available regarding habitat use by juvenile ABT (Brill et al 2002; Galuardi and Lutcavage 2012; Druon et al 2016). Juvenile ABT may exploit these deeper, cooler waters in order to feed—similar to the observed habitat use of Pacific Bluefin Tuna Thunnus orientalis, Skipjack Tuna Katsuwonus pelamis, and Yellowfin Tuna T. albacares (Marchal and Lebourges 1996; Kitagawa et al 2007b)—or to behaviorally thermoregulate, as seen in Yellowfin Tuna (Block et al 1997) Both juvenile and adult ABT have been documented as making excursions below the thermocline (Stokesbury et al 2004; Galuardi and Lutcavage 2012), the thermocline may act as a barrier to movement for adult ABT (Wilson et al 2005; Walli et al 2009). This relationship has not yet been examined for juvenile ABT
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