Bycatch in local fishery disrupts natural reestablishment of Eurasian otter in western Norway

Abstract

Lack of proper estimates of nonreported bycatch has made it difficult to evaluate the actual impact of bycatch in many local fisheries. For the Eurasian otter (Lutra lutra), there are no published estimates on the extent to which bycatch is unreported, despite nonreporting being a well-known issue. Through public outreach efforts in local news and media we collected information from citizen scientists on nonreported otter mortalities of a small-scale fishery in western Norway along the recent natural expansion front of otters. We compared this to deaths that were properly registered by local authorities. In total, cause of mortality was determined from 218 otters between 2003 and 2018. We found that the chances of a mortality being properly reported varied between type of death. Drowning in fyke and gillnets were the most common cause of mortality, and at least 61 and 69% of these deaths were never reported, respectively.The high level of bycatch occurring in the otters' current region of expansion is likely to have demographic impacts and hinder otter reestablishment in the area. Banning the use of fyke nets and setting a minimum fishing depth for gillnets would enhance otter recovery and simultaneously alleviate bycatch of other nontarget species in the region, while having little economic impact on a fishery which is mostly noncommercial. The case of the otter is a classic example of lack of communication between government agencies which have so far failed to establish platforms where issues like this can be discussed and solved by adequate law implementation.

Colony‐nesting gulls restrict activity levels of a native top carnivore during the breeding season

“…Although increased unpredictability of food sources during the breeding season is likely the leading cause of colony abandonment, heavy predation by invasive mink is believed to have exacerbated the rate of decline (Byrkjeland, 2015). At the same time, the otter has recently managed to reestablish throughout much of western Norway after having been extirpated from almost all central and southern parts of the country due to historical national bounties and extensive overhunting (Landa & Guidos, 2020). Little is known about the ecological connections between otters and gulls in Norway, although past studies indicate that gulls can be an important food source for a closely related species, the North American river otter Lontra canadensis during the breeding season (Hayward et al., 1975; Verbeek & Morgan, 1978).…”

Using Merged Pre-Fishery Abundance as a Parameter Evaluating the Status of Atlantic Salmon and Anadromous Brown Trout Populations: A Norwegian Case Study

“…There are several predators known to be feeding on juvenile Atlantic salmon and anadromous brown trout. Some of the most common predators, the Eurasian otter (Lutra lutra), Eurasian goosander (Mergus merganser), red-breasted merganser (Mergus serrator) are, however, distributed in all of the eight regions [55][56][57] and are most likely not responsible for the observed differences in the PFA among regions. Unlike the Atlantic salmon, the anadromous brown trout have relatively short sea migrations [24,58], and are restricted to the fjords close to the rivers where they were hatched and grew up to smolt stage.…”

Newly developed exit options for European otters from fish fykes

“…Vehicle strikes are clearly the leading cause of mortality for Eurasian otters in most countries (Lafontaine & Liles, 2002; Rohner et al, 2022). However, drowning‐associated mortality indicated fairly high figures in Finland between 1967 and 1991 (40.6% [ n = 41], Skarén, 1992), in Denmark between 1979 and 1993 (32.5% [ n = 63], Madsen et al, 1999), in Ireland between 1982 and 1992 (14% [ n = 87], O'Sullivan & Fitzgerald, 1995) and in Hordaland County, Norway, between 2003 and 2018 (57.3% [ n = 125], Landa & Guidos, 2020). Nevertheless, the number of otters drowning in fish traps in East Germany between 1957 and 1998 (6% [ n = 64] in Mecklenburg‐Western Pomerania, Saxony‐Anhalt, Brandenburg, Hauer et al, 2002) and in Hungary between 1999 and 2006 (0.8% [ n = 1], Lanszki et al, 2008) was significantly lower.…”