Influence of Spawning Ground Dynamics on the Long-Term Abundance of Japanese Flying Squid (Todarodes pacificus) Winter Cohort

Japanese flying squid (Todarodes pacificus) is one of the most commercially important resources in the Pacific Ocean and its abundance is largely affected by environmental conditions. We examined the influence of environmental factors in potential spawning grounds of the winter cohort, approximated from Japanese and South Korean catch and catch per unit effort (CPUE) data of Japanese flying squid. Annual spawning ground dynamics were constructed using sea surface temperature (SST), submarine elevation and mean Kuroshio axis data from 1979 to 2018. Based on these information, we generated a suite of spawning ground indices including suitability SST-weighted area of potential spawning ground (SSWA), mean values (January–April) of suitable SST (MVSS), and the meridional position (MP) of SST isolines (18–24°C). Comparable interannual-decadal variability patterns were detected between the squid abundance and spawning ground indices, with abrupt shifts around 1990/1991 and in recent decades. In particular, the Pacific Decadal Oscillation is negatively correlated with spawning ground indices, suggesting its role in regulating the environmental dynamics in the area. Further, the gradient forest model underpinned the importance of SSWA, SSWA_Lag1 and MVSS_Lag1 on squid abundance. The CPUE is also shown to be a better abundance index than the annual catch in modeling the species’ response to environmental variability in its spawning grounds. Our findings suggest that it is imperative to pay more and timely attention to the relationship between the abundance of Japanese flying squid and environmental changes, especially under adverse environmental conditions.

Current state of resources for japanese flying squid Todarodes pacificus in the northwestern Tatar Strait (Japan Sea)

Data on commercial catches of japanese flying squid Todarodes pacificus in the northwestern Tatar Strait in 2003–2019 are analyzed. To assess the resours status in the study area, the relative number (individuals per jigger winch per hour) and biomass (kilograms per vessel per day) marks recognized to be the most applicable winch per hour or the catch in kg per vessel per day. The average CPUE value was 35.6 ± 3.6 ind./winch/hour; increasing trend of CPUE is observed (α = 1.5 ± 0.6, r2 = 0.3, p < 0.03). The squid abundance decreased slightly in the last 2 years, with CPUE decreasing to 28 ind./winch/hour in 2019, though the squid biomass was relatively stable (average CPUE 582.0 ± 45.8 kg/vessel/day) — decreased number of caught individuals was compensated by individual body weight increasing. Long-term tendency to the body weight increasing was noted: the average body weight was 205.0 ± 4.0 g in 2004, 256.0 ± 3.5 g in 2012, and 297.0 ± 6.3 g in 2019. Possible climate change influence on the squid population was discussed. Because of warming in the reproductive area of T. pacificus in the southern Japan Sea, SST in the spawning period reached 20–25 оC and exceeded the value optimal for reproduction and larvae development (15–23 оC), so the squid abundance decreased. On the contrary, in the northern Japan Sea (in the Tatar Strait) the warming caused better conditions for the squid feeding: the higher zooplankton biomass in this area was observed under SST 13–18 оC that is reached every year recently. On the other hand, the Tsushima Current intensifying promoted active migrations of T. pacificus to the northwestern Tatar Strait. These factors of climate warming ensure favorable environments for northward migrations of T. pacificus and forming of dense feeding aggregations in the northwestern Tatar Strait that allows to expect good conditions for the squid fishery in this area in the nearest future.

PEMODELAN BERBASIS AGEN (ABM) UNTUK PENGELOLAAN AKTIVITAS MIGRASI MUSIMAN NELAYAN ANDON CUMI-CUMI DI PULAU SALURA

Perikanan cumi-cumi di Pulau Salura dibentuk oleh adanya agen nelayan andon, penduduk lokal, serta sumberdaya cumi-cumi. Kehadiran nelayan andon yang melakukan migrasi musiman dari Tanjung Luar di Pulau Lombok sampai ke Pulau Salura dengan aktivitas penangkapan cumi-cumi menjadikan sistem perikanan cumi-cumi ini menjadi berbeda dengan daerah lain. Intensitas migrasi dari nelayan andon yang tinggi berpengaruh terhadap perilaku penduduk lokal, serta kelimpahan sumberdaya cumi-cumi yang ada. Tujuan dari penelitian ini adalah mengkaji model pengelolaan aktivitas migrasi musiman dengan pengaturan alat tangkap yang dibawa. Metode yang digunakan adalah dengan pemodelan berbasis agen (ABM/Agent Base Model) melalui perangkat lunak Netlogo 6.2. Hasil penelitian menunjukkan bahwa pengaturan jumlah unit kapal yang terlibat dalam enangkapan cumi-cumi dalam waktu satu tahun harus diatur. Terdapat sembilan periode migrasi musiman yang dilakukan,sehingga model pengaturan jumlah unit kapal yang optimal untuk dapat menjaga kelimpahan cumi-cumi dan jumlah panenan nelayan adalah sebanyak 18 unit kapal setiap tahunnya. Populasi kelimpahan cumi-cumi yang dihasilkan sebesar 330 kuintal dengan masa regenerasi 42 hari, dan menghasilkan jumlah panenan sebesar 913 kuintal. (Agent Base Model For Seasonal Migration Activity of Squid Andon Fishers at Salura Island)Squid fishery system at Salura Island maked by multiple agent, as andon fishers, local peoples and squid resources. The presence of andon fishers who seasonally migrate from Tanjung Luar of Lombok Island to Salura Island with squid fishing activities makes the squid fishery system is to be different from other regions. The intensity of the migration of high andon fishers affected the behavior of the local population, as well as squid abundance of resources available. The purpose of this study was to manage the number of ships or fishing gear.The method is agent-based modeling (ABM / Agent Base Model) by used Netlogo 6.2 software. The results showed that the behavior of the agent can be analyzed from behaviors and activities. Setting the number of ships involved in catching squid in a year should be set. There are nine periods of seasonal migration is done, so that the optimal number of ships to be able to maintain the abundance of squid and the number of fishers are harvesting as many as 18 ships annually. The abundance of squid produced by 330 quintal with 42-day period of regeneration, and the squid harvest is 913 quintal.