First use of archival transmitters to track migrating freshwater eels Anguilla dieffenbachii at sea

Abstract

The spawning grounds of the New Zealand longfinned eel Anguilla dieffenbachii are unknown, but thought to be in the tropical region of the south Pacific Ocean. To determine whether pop-up tags could be used to provide information on the swimming speed and direction of migrating eels at sea, 4 female eels (7 600 to 11 400 g) were equipped with archival pop-up tags that were preprogrammed to surface after either 2 or 3 mo. All 4 tags ascended successfully at straight-line distances ranging from 368 to 1000 km offshore of the east coast of South Island, New Zealand. These estimated migration pathways showed that the eels moved substantial distances along inshore areas before moving offshore and eastward. There was no evidence of the expected northeast movement to tropical waters. Average swimming speed of all eels ranged from 15.1 to 31.3 km d

Survival and progression rates of large European silver eel Anguilla anguilla in late freshwater and early marine phases

“…The eels showed an increasing progression rate as they proceeded downriver and through the fjord, and it is possible that they increase migration speeds further when they approach the open ocean. Considerably higher short-term individual progression rates have been documented (mean 0.7 m s sion speed in the present study is in line with many other studies over longer migration distances (Tesch 2003) and also progression speeds in the ocean of European eel (Aarestrup et al 2009) and longfinned eels Anguilla diffenbachii (Jellyman & Tsukamoto 2002. Eel migration seems to be influenced by different environmental factors (e.g.…”

Performance of pop-up satellite archival tags

“…Crimps used to construct tethers were stainless steel. Brass crimps like the ones used in Jellyman & Tsukamoto (2002) promote electrolysis, which could interfere with the PSAT's detachment mechanism.…”

“…tag head). Drag, chafing, abrasion, vibration, and movement of tether and tag head (and possibly wicking action of the tether) most likely delay tag-insertion wound healing, thereby creating opportunity for infection, inflammation, tissue necrosis, and eventual PSAT shedding (Roberts et al 1973a,b,c, Borucinska et al 2001, Jellyman & Tsukamoto 2002, Thorsteinsson 2002, De Metrio et al 2004, Grusha & Patterson 2005, Wilson et al 2005. Our best-fitting retention models indicated that nylon tag heads were more likely to detach early than other types of tag heads, but other factors were also important; tag head type was strongly associated with tagger, tether material, location, and species/habitat class.…”

“…Battery failure (Seitz et al 2003, Hays et al 2007, Weng et al 2007) and antennae damage (Do meier 2006) have been responsible for the former, whereas mechanical failure of the nose cone pin and tethers has been identified as cause of early detachment (Domeier et al 2003, Stokesbury et al 2004, Wilson et al 2005. A variety of other causes have also been hypothesized for early detachment: increased drag as a result of biofouling (Gunn et al 2003, Kerstetter et al 2004, Benson & Dutton 2005, Hays et al 2007); infection and tissue necrosis at the site of the implanted anchoring device (Jellyman & Tsukamoto 2002, De Metrio et al 2004, Wilson et al 2005; entanglement, and social and sexual behaviors of the tagged individuals (Swimmer et al 2002, Thorsteinsson 2002.…”

Vertical migrations may control maturation in migrating female Anguilla dieffenbachii

“…In the present study, the tag weight was ~1% of body weight, so the eels were assumed to be large enough to carry a popup tag. Two previous studies using these tags on migrating (silver) female Anguilla dieffenbachii (Jellyman & Tsukamoto 2002 have recorded significant diel vertical and offshore movements, but tags failed to remain attached for the duration of the programmed time (up to 7 mo). Further, the daytime diving behaviour meant that insufficient light recordings were available for subsequent estimation of locations of eels and tracking of migration routes.…”