ICES CM 2013/O:10

Seasonal offshore‐onshore migration of anglerfish Lophius piscatorius in Faroese waters

Lise H. Ofstad (1), Petur Steingrund (1) and Torstein Pedersen (2) (1) Faroe Marine Research Institute, Nóatún, Tórshavn, Faroe Islands; (2) Faculty of Biosciences, Fisheries and Economics, Department of Arctic and Marine Biology, Tromsø, Norway. Presenter contact details: [email protected], Phone +298 353900

Summary Migration pattern of anglerfish in Faroese waters is poorly known. Seasonal migration and vertical movement of anglerfish was investigated by mark‐recapture methods, including data storage tags, and compared to information from traditional tags, scientific trawl surveys and the commercial fishery. A distinctive seasonal offshore‐onshore migration pattern was observed as anglerfish occupied shallow waters (<200 m) during summer and deeper waters (>300 m) in winter. This seasonal movement was most pronounced for large (>70 cm) sexually mature fish, hence, indicating that spawning occurs in deep waters during winter and feeding in shallow waters during summer. Approximately 5% of the total data storage tag recordings showed more than 5 m vertical movement between two following hourly recordings. There was a seasonal and diurnal difference in vertical migration activity as anglerfish was more vertically active in winter than summer and during night time than day time. This indicates light intensity and day length influence vertical migration of anglerfish. Anglerfish was mostly located in relatively warm waters (6.5–11ºC) and seldom located in temperatures colder than 4ºC.

Introduction During the last decade, anglerfish in Faroese waters have become highly exploited and commercially important for the Faroese fishing fleet (Ofstad, 2013). Despite commercial value many aspects of their life history remain unknown, e.g. horizontal and vertical migration pattern. Many fish stocks display a seasonal migration pattern which has been related to spawning‐ and/or feeding activities, or as a response to thermal conditions. Spawning and feeding migrations have been observed among Lophius species in the northeast Atlantic (Laurenson et al., 2005). The aim here is to investigate whether anglerfish in Faroese waters undertake seasonal migrations and if they display vertical movement activity, by investigating if there were a seasonal difference in: i) preferred depth, ambient temperature and vertical activity level of anglerfish tagged with data storage tags, ii) displacement distance and location of recaptures of anglerfish tagged with conventional tags, iii) depth‐ and temperature distribution, catch rates and spatial distribution as observed in trawl surveys and spatial distribution of commercial trawl and gillnet fishery effort based on logbooks.

Materials and methods The mark‐recapture program for anglerfish (>70 cm long) caught from gillnet north of the Faroe Islands took place during two separated periods, in 2006 and 2009–2011. The conventional tags were t‐ anchor tags (Floy tag Inc., Seattle, USA) placed in tail muscle of 436 anglerfish (10% recapture). The data storage tags (DSTs, Star‐Oddi, Iceland) registered date, time, depth (pressure) and temperature, and were set to log at least once per hour. During the second period DSTs were inserted subcutaneously dorsally in 55 fish (27% recapture). The tags were marked with a coding number and contact information for the Faroe Marine Research Institute. For detailed description of mark‐ recapture methods see Ofstad (2013). Here, DSTs data from anglerfish with time at liberty longer than three months were used and the results were calculated by pooling the data from these 10 anglerfish. Vertical activity movement of anglerfish was defined as a depth difference of more than 5 m between subsequent hourly recordings. A vertical activity index (%) was calculated as; total number of vertical activity registrations*100/total registrations for time of day in one particular season. Data from traditional tagging, scientific surveys and commercial logbooks were used for comparisons. ICES CM 2013/O:10

_ _ _ Results and Discussion 0 _ _ _ _ _ A) _ _ _ _ In Faroese waters, DST data show that large (>70 cm) 50 mature anglerfish perform an offshore spawning 100 migration in autumn into deeper waters (>300 m) and 150 _ _ migrate back to shallower inshore areas (<200m) in 200 ______250 _ _ spring to feed (Figure 1A; Ofstad, 2013). The migration ______300 _ _ pattern observed from DST tagging fits well with results _ _ Depth (m) _ _ 350 _ _ of anglerfish seasonal location and depth as reported by _ 400 _ _ _ traditional tags, in scientific surveys and the commercial _ 450 _ _ fishery, where: i) a spawning area is located southwest _ 500 _ of the Faroe Plateau where bottom depth is 550 approximately 300–400 m, ii) large fish have higher Jan Mar May Jul Sep Nov feeding rates in summer in areas shallower than 200 m, Month iii) recaptured anglerfish from conventional tagging 20 B) Nov−Feb showed longer migration distances from the tagging site 18 Mar−Apr in winter than in summer, iv) data from scientific survey May−Aug 16 Sep−Oct showed that anglerfish larger than 70 cm had a deeper 14 distribution in February and March than in August, and 12 v) commercial logbook data display how main fishing 10 locations where deeper in winter than in summer 8 (Ofstad, 2013). 6

4 Vertical activity of anglerfish varied with season and activity index (%) Vertical 2 was higher from autumn to spring (September to April), 0 at the same time of year when fish migrate between spawning and feeding areas, than during summer 048121620 Time of day (hour) (Figure 1B). Time of day also influenced vertical activity of anglerfish as they showed less activity during Figure 1. A) Anglerfish depth distribution per daylight hours. Diurnal migration could be influenced month. The black line shows the median, the box represents the upper and lower quartile, the by feeding. This seasonal and diurnal migration pattern error bars show upper and lower extremes is probably triggered by the light intensity, rather than (excluding outliers) and the short grey the sea temperature, since there was a very strong, horizontal lines show outliers. B) Average negative correlation between the hours of high vertical vertical activity index (%) plotted versus hour of activity during the day each month and the mean light the day for various seasons. The error bars show 95% CI. The data are from pooled DST data of intensity (Ofstad, 2013). Anglerfish were seldom 10 large (>70 cm) anglerfish. distributed or caught in temperatures colder than 4ºC, indicating that anglerfish distribution is temperature dependent (Ofstad, 2013).

Anglerfish can performed extensive vertical migrations, moving from depths of 100–400 m to near surface (0–50 m depth) in a short time period (few hours) indicates that anglerfish can occupy the pelagic layer (Ofstad, 2013) as showed for L. americanus (Rountee et al., 2008). As the vertical activity of anglerfish in Faroese waters is low (approximately 5% of registrations) (Ofstad, 2013) they could increase their movement efficiency and capacity by migrating with the dominant ocean currents during their seasonal migrations, as hypothesised by Laurenson et al. (2005).

References Laurenson, C.H., Johnson, A., and Priede, I.G. 2005. Movements and growth of monkfish Lophius piscatorius tagged at the Shetland Islands, northeastern Atlantic. Fisheries Research, 71(2): 185–195. Ofstad, L.H. 2013. Anglerfish Lophius piscatorius L. in Faroese waters. Life history, ecological importance and stock status. PhD Thesis, University of Tromsø, Norway, 108 pp. Rountree, R.A., Gröger, J.P., and Martins, D. 2008. Large vertical movements by a goosefish, Lophius americanus, suggests the potential of data storage tags for behavioral studies of benthic fishes. Marine and Freshwater Behaviour and Physiology, 41(1): 73–78.