The Stock Status of Skipjack Tuna (Katsuwonus pelamis) in Tomini Bay and Its Surrounding Areas, Indonesia

Skipjack tuna (Katsuwonus pelamis) is an essential part of tuna, skipjack tuna, and mackerel tuna trades in Indonesia as the species is an economic commodity with export value. Tomini Bay is one of the areas in Indonesia with intensive skipjack tuna exploitation activities using purse seine fleets. Such a high fishing rate requires management efforts to maintain the species population’s sustainability. This study was conducted in April 2018–December 2019 at a fish landing site in Gorontalo City with a total sample of 8,833 skipjack tunas. The population dynamics, recruitment, and utilization rate were analyzed using FISAT II application and ELEFAN program. The results showed that the length at first capture (Lc) was 31.8 cmFL (in 2018) to 32.2 cmFL (in 2019) at around 1.3 year old. The fish recruitment occurred all year long, peaking in May at 16.12%. In addition, the utilization rate (E) of the species was 0.47, meaning that the species was already moderate to fully exploited. The suggested practical management efforts to maintain the population of the skipjack tunas in the area are to stop the fishing efforts from growing and control the size of the mesh for fishing.

Spawning stock biomass modulation of environment - recruitment relationship in a marginal spring spawning herring (Clupea harengus membras) population

Scientific interest in the dynamics of fish recruitment dates back to the beginning of the 20th century. Since then, several studies have shown that the environment may have a stronger effect on recruitment (R) compared to that of the spawning stock biomass (SSB). By combining a suite of methods designed to detect the non-linear, non-stationary and interactive relationships, we have re-evaluated the potential drivers and their interactions responsible for the multiannual dynamics of the recruitment dynamics of the Gulf of Riga (Baltic Sea) spring spawning herring population at the longest time-span to date (1958-2015) allowing coverage of variable ecosystem conditions. R was affected significantly by prey density and the severity of the first winter. Although SSB was not a good predictor of R, adding interaction with SSB significantly improved the model, hence the effect of the two environmental variables on R was modulated by SSB. While temporal changes in the environment-R relationship were generally gradual, several abrupt changes were evident in the strength of these relationships. In addition, non-stationary, linear and non-linear relationships were observed.

Recruitment of coral reef fishes along a cross-shelf gradient in the Red Sea peaks outside the hottest season

Knowledge on the early life history, ecology, and biology of marine species is crucial for future projections of the resilience of coral reef ecosystems and for adequate management strategies. A fundamental component of population dynamics is the recruitment of new individuals, and in some marine populations, this may be a limiting factor. Recruitment peaks of coral reef fishes commonly occur during the warmer months of the year in many subtropical and temperate locations worldwide. In the Red Sea, very little is known about the influence of temperature on reproductive patterns of coral reef fishes and studies on recruitment are missing. The Red Sea is one of the hottest and most isolated tropical seas in the world. We hypothesized that sea surface temperatures (SSTs) during the Red Sea’s hottest season may exceed the optimum for successful recruitment of some coral reef fishes, which therefore has to occur during other, cooler seasons, unlike recruitment among coral reef ecosystems around the world. We identified taxa among fish recruits by matching mitochondrial DNA sequences (using COI, commonly known as “barcoding”) and assessed potential biological and environmental drivers of recruitment. We studied three reefs located along a cross-shelf gradient for 12 consecutive months in the central Red Sea to capture seasonal changes in biotic and abiotic parameters along this gradient. Our results indicated that recruitment peaks did not occur during the hottest SSTs for most taxa, especially at the hottest inshore and mid-shelf reefs, and identified fish recruitment to be mainly and strongly correlated with the biomass of planktonic invertebrates. Moreover, temporal patterns of fish recruitment differed within and among taxonomic families among the reefs.