Vertical Movement and Behavior of the Ocean Sunfish, Mola Mola, in The

Vertical Movement and Behavior of the Ocean Sunfish, Mola Mola, in The

JEMBE-49259; No of Pages 9 Journal of Experimental Marine Biology and Ecology xxx (2010) xxx–xxx Contents lists available at ScienceDirect Journal of Experimental Marine Biology and Ecology journal homepage: www.elsevier.com/locate/jembe Vertical movement and behavior of the ocean sunfish, Mola mola, in the northwest Atlantic Inga F. Potter ⁎, W. Huntting Howell Large Pelagics Research Center, Department of Biological Sciences, Spaulding Life Sciences Bldg., University of New Hampshire, Durham, NH 03824, USA article info abstract Article history: Pop-up satellite archival tags (PSATs) were attached to 31 ocean sunfish, Mola mola. in the Northwest Atlantic Received 30 May 2010 between 2005 and 2008, in order to examine their vertical movement and behavior. Tags remained attached Received in revised form 11 October 2010 from 7 to 242 days, with a mean attachment period of 107.2±80.6 (SD) days. Fish spent greater than 30% of Accepted 13 October 2010 their time in the top 10 m of the water column, and over 80% of time in the top 200 m. The maximum depth Available online xxxx recorded by any fish was 844 m. Temperatures experienced by tagged fish ranged from 6 to 30 °C. Vertical behavior of M. mola changed over short-term and seasonal scales. Ocean sunfish in northeastern US waters in Keywords: Mola mola the summer months inhabited shallower depths and spent more time at the surface than those that moved Northwest Atlantic south in the winter and spring. This shift from shallow to deeper depths was especially apparent when fish Ocean sunfish entered the Gulf Stream, where they spent little time at the surface and dove to depths of 400–800 m. A diel Pop-up satellite tag pattern was observed in vertical behavior. Tagged fish spent more time at depth during the day and inhabited Vertical movement shallower waters at night. There was no observed relationship between the amount of time per day that fish spent in cold water (b10 °C) and the amount of time fish spent near the surface (0–6 m), indicating a lack of evidence for M. mola basking at the surface as a mechanism for behavioral thermoregulation. © 2010 Elsevier B.V. All rights reserved. 1. Introduction diel pattern has been observed in the vertical movements of ocean sunfish with nocturnal movements limited to near-surface waters and The ocean sunfish, Mola mola, is a large pelagic species distributed diurnal vertical movements including repeated dives below the worldwide in both temperate and tropical oceans. A member of the thermocline (Cartamil and Lowe, 2004; Thys et al., 2007; Sims et al., family Molidae in the order Tetraodontiformes, M. mola is known for 2009). This diel pattern, observed in other large pelagic fishes (blue its unique body shape, large size (reaching 4.2 m and weighing up to sharks, swordfish and tunas) (Carey and Scharold, 1990; Block et al., 2300 kg), and atypical anatomy (Gregory and Raven, 1934; Norman 2001; Sims et al. 2003), is thought to be related to prey acquisition. In and Fraser, 1949; Fraser-Bruner, 1951; Bass et al., 2005). Sunfish are addition to prey acquisition and thermocline depth, other factors have valued food fish in Asia and comprise a large portion of bycatch in been suggested as physiological influences on M. mola's diving Pacific and Mediterranean commercial fisheries (Silvani et al., 1999; behavior, including the depth of the DSL or chlorophyll maximum, Macias and de la Serna, 2002; Cartamil and Lowe, 2004; Lovgren, changes in temperature, and a decreased oxygen concentration at 2004; Thys, 2005). M. mola is a common resident of the offshore depth (Thys, 2003; Cartamil and Lowe, 2004; Fulling et al., 2007). waters of the Northwest Atlantic during the spring and summer Ocean sunfish were so named for the common behavior of lying on months, with an estimated summer population of 18,000 (Kenney, their sides near the surface, appearing to “sunbathe”, which has been 1996). Little is known about M. mola's basic ecology, distribution, or suggested to be a mechanism of “thermal recharging” after deep dives population dynamics, and the global status of the species is unknown. in cold water (Thys, 2003; Cartamil and Lowe, 2004), or to solicit Few studies have been conducted on the movement or behavior of cleaning/parasite removal from above the surface by seabirds, or M. mola, and there is no such information on the species in the below by fishes (Pope et al., 2010). northwestern Atlantic. Results from previous tagging studies indicate A tagging study on M. mola in the North Pacific found that dive they spend the majority of their time in the top 50 m of the water behavior was dependent on both location of the fish and time of year. column, with occasional dives to deeper depths (400–600 m) (Thys, As fish moved south into the autumn and winter months, their time at 2003; Cartamil and Lowe, 2004; Thys et al., 2007; Sims et al., 2009). A greater depths increased. As the fish returned north, they resumed a pattern of shallow diving (Thys, 2003). Recent studies of ocean sunfish in both the North Pacific and eastern North Atlantic Oceans found a seasonal pattern of migration related to sea surface ⁎ Corresponding author. PO Box 4524, Portsmouth, NH 03802, USA. Tel.: +1 603 380 5707; fax: +1 603 862 3784. temperatures/thermal tolerance and decreasing chlorophyll levels E-mail address: [email protected] (I.F. Potter). (Thys et al., 2007; Sims et al., 2009). 0022-0981/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jembe.2010.10.014 Please cite this article as: Potter, I.F., Howell, W.H., Vertical movement and behavior of the ocean sunfish, Mola mola, in the northwest Atlantic, J. Exp. Mar. Biol. Ecol. (2010), doi:10.1016/j.jembe.2010.10.014 2 I.F. Potter, W.H. Howell / Journal of Experimental Marine Biology and Ecology xxx (2010) xxx–xxx The present study is the first to examine the vertical movement geolocation data, were used to identify the location of tagged fish. and behavior of M. mola in the northwestern Atlantic. The study's Depth–temperature plots were created from the raw PSAT data in R objectives were to attach pop-up satellite archival tags (PSATs) to using methods of Galuardi (unpublished). For some analyses, the fish ocean sunfish during the summer and autumn off the coast of New were divided into two groups—north and south of 35°N latitude, to England in order to examine behavior and identify movement separate “northern/mid-Atlantic fish” and “southern fish,” because patterns of M. mola in the region. when they moved south of about 35°N latitude, their vertical behavior changed. Those fish defined as “northern/mid-Atlantic fish” or 2. Materials and methods “northern” fish never moved south of 35°N (n=12). Those defined as “southern fish” were tagged in New England and moved south of 2.1. Tagging 35°N at some point during the course of their tagging period (n=11). Vertical behavior of fish was examined relative to water temperature Between 2005 and 2008, 31 pop-up satellite archival tags (PSATs: by comparing depth data from individuals when in warm water model PTT-100, Microwave Telemetry, Columbia, MD, USA) were (N24 °C) to that of the same individuals in offshore, cooler water deployed on ocean sunfish, M. mola, in the Northwest Atlantic. (b24 °C). The basking behavior of M. mola was examined by analyzing, Twenty-nine were deployed during the summer and autumn for each fish, the amount of time per day spent in cold water (b10 °C) (August–October) of 2005, 2006, or 2007. Fish were tagged in the and the amount of time during that same day that fish spent at the Gulf of Maine (n=7) and in shelf waters to the south and east (within surface (0–6 m). 80 km) of Nantucket Island (n=22). Five fish were tagged in 2005 as a pilot study. Fourteen fish were tagged in 2006, and 10 fish were 3. Results tagged in 2007. Two additional fish were tagged in March 2008 in shelf waters off the coast of Georgia, USA. PSATs were prepro- Of the 31 PSATs deployed, 25 successfully reported data back to grammed to release either five or eight months after deployment. Argos. Fig. 1 shows a map of the deployment and endpoint locations Fish were tagged from commercial tuna vessels (F/V Peregrine, F/V for all 25 tags. A summary of the dates and locations of the start and Tenacious; n=10) and a charter fishing vessel (F/V Monomoy; n=19) end of each tag deployment, days at liberty, distance traveled, and in the waters off the northeastern United States, and from a research percent data reported is provided in Table 1. Tag attachment periods vessel in Georgia (R/V Margaurite, Georgia DNR). Fish basking at the ranged from 5 to 242 days. Eighteen tags were attached for 50 days or surface were approached by the vessel, and tags were attached via a more, 10 of those were attached for 150 days or more, and 4 of them modified wooden harpoon tagging pole, 2.5 m in length. Monofila- were attached for at least 240 days. Mean attachment period of all the ment tethers (25 cm long, 250-lb test) were used to attach the PSATs tags reporting data was 107.2±80.6 days (SD), and mean data to black nylon umbrella darts (darts designed and produced by reported was 69.7±33.1% (SD) (n=25). Two tags with data retrieval Michael Domeier, Marine Conservation Science Institute).

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