Optical and acoustic camera observations of the behavior of the Kuril harbor seal Phoca vitulina stejnegeri after invading a salmon setnet

Abstract

It has previously been confirmed that Kuril harbor seals Phoca vitulina stejnegeri cause damage to the chum salmon Oncorhynchus keta set-net fishery along the east coast of Hokkaido, Japan, but the level of damage has increased markedly with the recovery of their population in recent years. In this study, we attached an optical camera (TrawlCamera) and a Dual-Frequency Identification Sonar (DIDSON) acoustic camera to a set net to observe the behavior of seals as they invaded the set net and the number of salmon inside the net to help inform the development of modified fishing gear. Salmon were observed at all times during daytime with the TrawlCamera, while seals were only observed once. Observations using the DIDSON in its low-frequency mode confirmed that the behavior of seals became vigorous from around sunset to nighttime within the recording time (15:30-21:00). Observations with the DIDSON's high-frequency mode showed that the overall lengths and body widths of seals ranged from 1.0 to 1.6 m and 0.15 to 0.35 m, respectively, while their swimming speeds ranged from 0.4 to 2.6 m/sec, increasing around sunset and declining into the night. These results imply that seals mainly invade the set net from evening to nighttime to predate on salmon.

When large marine predators feed on fisheries catches: Global patterns of the depredation conflict and directions for coexistence

“…Changing perceptions is, in fact, a critical process on the road to coexistence with depredating predators (Cummings, Lea, & Lyle, 2019; Frank, 2016; Guerra, 2019). This is challenging given the complexity of factors influencing perceptions, as including cultural environments, history, personal experiences and sometimes beliefs and myths (Dickman, 2010).…”

Using fish behavior to design a fish pot: Black seabream (Spondyliosoma cantharus) case study

“…Some development for trawl gear already contributed to reduce fishing gear impacts and increase their selectivity by providing rapid, accurate and standardized data on fish behavior in relation to gear (Robert et al, 2020). In parallel, the development of acoustic imaging would overcome dark and turbid conditions to describe fish behavior in relation to fishing gear on a longer period of time (Rose et al, 2005;Fujimori et al, 2018). It is especially relevant for species with diurnal feeding habit (eg.…”

Monitoring fish using imaging sonar: Capacity, challenges and future perspective

“…Marine mammals usually invade the fishing gear where fish gather for predation, causing damage to fishing gear and reducing landed catch (Lunneryd et al, 2003). The invading behaviour of seals is explored by observing the diel activity pattern of seals to support the prevention strategy planning and fishing gear modification (Fujimori et al, 2018; Nichols et al, 2014).…”

“…The responses of fish to the fishing gears are investigated to evaluate the efficacy and selectivity of fishing gear and aid its design (Williams et al, 2013). Typically, the movement in the net (Kang et al, 2020; Williams et al, 2013), avoidance of the trawl (Jůza et al, 2013; Rakowitz et al, 2012) and occupation of the fishing gears (Fujimori et al, 2018; Nichols et al, 2014) are studied with high‐frequency MFLS.…”