Vertical migrations may control maturation in migrating female Anguilla dieffenbachii

Abstract

The marine spawning area of the New Zealand longfin eel Anguilla dieffenbachii is unknown. The present study used 3 popup tags to obtain information on the offshore swimming behaviour and possible swimming directions and destination of migrating eels. All 3 eels showed very consistent behaviour and underwent daytime dives to depths of 600 to 900 m, where they experienced temperatures of 6 to 7°C. These dives were followed by nighttime ascents to depths of 200 to 300 m. From the consistency of these dives, we propose that eels are using regular exposure to cool temperatures to regulate the rate of maturity. While swimming at depth could also reduce predation, the increased pressure would stimulate development of the ovaries, something mediated by ascent to shallower water. Comparisons of ascent locations and swimming speeds are consistent with spawning in the tropics, possibly in the South Fiji basin. KEY WORDS: Anguilla dieffenbachii · Freshwater eel · Diving · ThermoregulationResale or republication not permitted without written consent of the publisher

Development and testing of attachment methods for pop-up satellite archival transmitters in European eel

“…Further, European eel biting at tag surgery sites has previously been observed [18]. The spectacular and frequent vertical migrations observed during the ocean migration of both European eel and longfin eel that cover several hundred meters depth [1,13] are not likely to be tagging effects on behavior, but are most likely their natural migration behavior. This is because the vertical migration behavior was consistent over extended periods of time during the ocean migration and not the type of short-term phenomenon as the behavioral reactions to tagging observed in the present study.…”

“…One Figure 4 Illustration and photos of the Jellyman and Tsukamoto tagging method used to attach pop-up satellite archival transmitters to European silver eel. The method is slightly modified from the tagging method described by Jellyman and Tsukamoto [11][12][13]. loop had a horizontal angle but was bent up 90°, and the other loop was vertical ( Figure 5).…”

“…However, field studies using this method in longfin eel (Anguilla dieffenbachia) have also shown premature loss of transmitters, with tags being retained from only a few days up to 60 to 90 days for most fish, with a maximum attachment period of 161 days [11][12][13]. The main problem with this method was keeping the plates aligned flat on the side of the eels without being dragged upwards and digging into the muscle.…”

“…This tagging method was described and used by Jellyman and Tsukamoto for attaching PSATs to longfin eel [11][12][13]. Three circular plastic discs were prepared, two for attachment on each side of the eel (each with one hole) and one for the back (with two holes) keeping the tag in place (Figure 4).…”

Behaviour of stocked and naturally recruited European eels during migration

“…Tesch 1978, Aarestrup et al 2009) as well as, more recently, other Anguilla species (Jellyman & Tsukamoto 2010, Béguer-Pon et al 2012, Schabetsberger et al 2013). There was no significant difference in the depths that eels occupied during the day or night, or in the depth range, between stocked or naturally recruited eels, i.e.…”