FISHERIES OCEANOGRAPHY Fish. Oceanogr. 23:1, 65–82, 2014 Movements, behavior, and habitat utilization of yellowfin tuna (Thunnus albacares) in waters surrounding the Revillagigedo Islands Archipelago Biosphere Reserve, Mexico KURT M. SCHAEFER,1* DANIEL W. FULLER1 influence on the movements, behavior, and habitat AND GABRIEL ALDANA2 utilization of yellowfin in this area. 1 Inter-American Tropical Tuna Commission, 8604 La Jolla Key words: behavior, habitat, movements, utilization Shores Drive, La Jolla, CA, 92037-1508, U.S.A. distributions, yellowfin tuna 2Instituto Nacional de Pesca, Centro Regional de Investigacio´n Pesquera, Calzada Sa´balo Cerritos s/n, contiguo Estero El Yugo, Mazatla´n, Sinaloa, c.p. 82010, Me´xico INTRODUCTION ABSTRACT Yellowfin tuna, Thunnus albacares, is a large, highly mobile pelagic species, distributed worldwide in sub- The movements, behavior, and habitat utilization of tropical and tropical seas, except the Mediterranean yellowfin tuna, Thunnus albacares, following capture Sea, and is of substantial socio-economic importance and release with archival tags in the Revillagigedo (Collette and Nauen, 1983; Miyake et al., 2010). Yel- Islands Archipelago Biosphere Reserve (RIABR), lowfin is a principal target species of a large interna- Mexico, are described from analyses of 16 578 days of tional purse-seine fishery in the eastern Pacific Ocean time-series data, downloaded from 52 archival tags (EPO), from which the average annual retained catch – recovered from yellowfin (78 173 cm in length and during 1981–2010 was about 240 000 metric tons – = 1.7 8.0 yr of age) at liberty from 93 to 1773 days (x (range: 84 000–412 000 metric tons) (Anonymous, – 411 days), collected during 2006 2012. An unscented 2011). Yellowfin were caught in the EPO by purse- Kalman filter model with sea-surface temperature mea- seine vessels during 2005–2009 from about 30°Nto surements integrated (UKFsst) was used to process the 20°S and from the coast of the Americas west to about archival tag data sets to obtain improved estimates of 150°W (Anonymous, 2011). geographic positions, most probable tracks (MPTs), Tagging experiments on yellowfin utilizing plastic and movement parameters. The MPTs indicate dart tags (PDTs) since the early 1950s throughout the restricted movements, low levels of dispersion, and EPO, appear to indicate that movements of tagged fish fidelity of yellowfin tuna to the RIABR. The median at liberty for more than 30 days tend to be restricted parameter estimates from the UKFsst model for errors to <1000 NM of their release positions (Schaefer, r r ° in longitude ( x) and latitude ( y) were 0.46 and 2008). In recent tagging experiments utilizing archival ° 1.84 , respectively, for directed movements (u and v) tags (ATs), rich data sets for evaluating spatiotemporal –0.05 NM dayÀ1 and –0.05 NM dayÀ1, respectively, 2 À1 movement patterns, and habitat utilization, for numer- and for dispersive movement (D) 117.99 NM day . ous large marine pelagic predators have been gener- Analyses of daily timed depth and temperature records ated (Block et al., 2011). ATs can vastly improve our resulted in the classification of the data into four dis- understanding of the movements, stock structure, tinct behaviors. There are significant differences behavior, and habitat utilizations essential for improv- among ages in the durations of Type I and Type II div- ing stock assessments. Current-generation ATs are ing behaviors and in the daytime and nighttime verti- capable of autonomous sampling of high-resolution cal habitat utilization distributions. The oceanography data for multiple years, providing opportunities to surrounding the RIABR appears to have a profound evaluate the influence of seasonal and inter-annual environmental variability and ontogenetic changes in movement patterns, behavior, and habitat utilization. *Correspondence. e-mail: [email protected] Furthermore, utilizing state-space models such as the Received 20 December 2012 unscented Kalman filter model with sea-surface tem- Revised version accepted 29 July 2013 perature (SST) measurements integrated (Nielsen © 2013 John Wiley & Sons Ltd doi:10.1111/fog.12047 65 66 K. M. Schaefer et al. et al., 2006; Lam et al., 2008) for analyses of AT geo- may be utilized to improve stock assessments through location data sets, can provide improved estimates of standardization of purse-seine and longline catch and geographic positions, most probable tracks (MPTs), effort data (Maunder and Punt, 2004; Maunder et al., and movement parameters. The movement parameters 2006). can subsequently be incorporated into population Yellowfin tuna tend to be more abundant in the movement models. A recent tagging experiment in vicinity of islands and seamounts, where there are which large numbers of yellowfin were released with commonly high concentrations of forage organisms, implanted ATs for several consecutive years off Baja than in the surrounding oceanic waters (Murphy and California, Mexico, demonstrated restricted move- Shomura, 1972). Biological productivity ranges from ments, quantified movement parameters, and eluci- moderate to low throughout the distributional range of dated behavior patterns and habitat utilization yellowfin in the EPO, except in regions of strong (Schaefer et al., 2011). upwelling, which includes some coastal zones, equato- Considering the restricted movements, and limited rial regions, the Gulf of Tehuantepec, and the vicinity mixing of yellowfin throughout the EPO, the develop- of islands and seamounts (Sund et al., 1981). Uda and ment of a spatially structured stock assessment model Ishino (1958) reported that eddying and upwelling with movements appears to be warranted, and is being occur on the down-current side of islands. Bakun developed by the staff of the Inter-American Tropical (1996) provided further description of such physical Tuna Commission (Bayliff, 2001). However, to oceanographic features as wakes on the down-current develop a scientifically valid spatially structured assess- side of islands and Taylor columns around seamounts, ment model of movement for yellowfin in the EPO, it which generate increased biological production in is necessary to better understand yellowfin stock struc- such areas. High concentrations of yellowfin forage, ture and obtain estimates of movement parameters including juvenile reef fishes, were observed within and life history characteristics from several spatial eddies around the Revillagigedo Islands, by the authors strata. This can be achieved, but requires large-scale of this paper, during tagging cruises in that area multi-year tagging studies utilizing ATs, conducted between 2006 and 2011. throughout the region of the EPO inhabited by yellow- Historically the catches of tunas around the Revilla- fin and exploited by commercial fishing vessels. gigedo Islands by commercial pole-and-line and purse- Field experiments to investigate vertical move- seine vessels were substantial (Carocci and Majkowski, ments and habitat of yellowfin in the EPO began with 1996). The Revillagigedo Islands have also historically studies using ultrasonic telemetry with acoustic tags been a popular destination for anglers targeting giant (Carey and Olson, 1982; Block et al., 1997). Those yellowfin tuna (Roecker, 2010). The government of studies indicated vertical movements of yellowfin to Mexico issued a presidential decree in 1994 creating be restricted predominantly to depths of the mixed the Revillagigedo Islands Archipelago Biosphere layer, but occasionally below the thermocline for short Reserve (RIABR), establishing a 6-nm ‘nucleus zone’ periods. More recently, ATs implanted in yellowfin surrounding each of the four islands, but allowed sport- released in a few different areas of the EPO have fishing within the reserve, subject to limits and con- yielded significant amounts of new and useful informa- straints, until March 2002 (Anonymous, 1994, 2004). tion on their vertical movements and habitat utiliza- Currently, sportfishing vessels with permits from the tion (Schaefer et al., 2009, 2011). These more recent Government of Mexico to operate in this area are studies indicate that vertical movements of yellowfin restricted to fishing outside the 6-nm zone, and Mexi- are not restricted to depths of the mixed layer, but can flag commercial fishing vessels are not permitted to consist of different diving patterns dependent on forag- fish within 12-nm of each of the four islands of the ing strategies, including repetitive bounce-diving RIABR. The RIABR was established not just for tuna behavior during the day to depths of 200–400 m while conservation but for the overall protection of a unique targeting prey organisms of the deep-scattering layer. and biologically diverse marine environment. In the equatorial EPO and off Baja California, Mexico, The objectives of this investigation are to quantify the AT data from yellowfin indicated that they could and elucidate the horizontal and vertical movements, spend up to 44 and 50%, respectively, of their time behavior, and habitat utilization of yellowfin released during the day below the thermocline (Schaefer et al., in the RIABR, based on analyses of 16 578 days of 2009; Schaefer et al., 2011). Determination of the time-series data, downloaded from 52 archival tags physiological and behavioral constraints, along with recovered from yellowfin (78–173 cm in length and the environmental variables that define habitat for yel- 1.7–8.0 yr of age) at liberty from 93 to 1773 days (x = lowfin, including depth and temperature distributions,