Effect of freshwater discharge from Namgang Dam on ichthyoplankton assemblage structure in Jinju Bay, Korea

The movement of fish eggs and larvae in bay and estuarine systems is affected by freshwater discharge. In this study, the assemblage structures of ichthyoplankton eggs and larvae were assessed for the first time in Jinju Bay, South Korea, to identify the spawning and nursery functions of the bay. Fish eggs and larvae and several environmental parameters were sampled monthly from April 2015 to March 2016 inside and outside of the bay. Within the bay we collected eggs and larvae from 25 and 35 species, respectively, indicating greater diversity than outside the bay, where we collected eggs and larvae of 20 and 28 species, respectively. Fluctuations in water temperature and salinity were larger inside than outside of the bay, and chlorophyll-a concentration was higher within the bay, likely due to discharge from the Namgang Dam, which causes water to flow from the inside to the outside of the bay. This process influences fish larva abundance, such that more larvae are found outside than inside the bay. We also found that 28 fish species use Jinju Bay as a spawning ground. For some species, the timing of egg and larva appearance differed inside and outside of the bay, suggesting that the timing of spawning may differ between the two environments.

Spawning aggregations of fish in Cabo Delgado, Northern Mozambique: An interview-based survey of artisanal fishers

Seasonal aggregations at specific sites are common among some fish species. Experienced fishermen know where and when these aggregations happen, often targeting these spawning sites to increase their catch. This strategy can further contribute to endangering the survival of these species, especially for those already threatened by other forms of pressure. This study contributes knowledge to the spawning aggregation of fish in the north of Mozambique following survey work conducted around Cabo Delgado Province in six coastal villages in 2016, 2017 and 2018. The objectives of the study were 1) to identify the species and sites of spawning aggregation and 2) to determine the timing of spawning aggregations. Data collection consisted of interviews targeting the most experienced fishermen to obtain information on these subjects. The results indicate that out of 124 fishermen interviewed, 59% had knowledge of spawning aggregations. The information collected from fisher interviews revealed that there are at least six spawning locations and at least eight species aggregate to spawn (Leptoscarus vaigensis, Lethrinus harak, Lethrinus nebulosus, Lethrinus obsoletus, Lethrinus olivaceus, Plectorhinchus gaterinus, Plectorhinchus schotaf, Siganus sutor). Only Siganus sutor was reported to spawn in at least one of the fishing areas used by every village. The timing of spawning aggregations most reported by fishermen was during the Kusi (South) monsoon period.

Evidence for temperature-dependent shifts in spawning times of anadromous alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis)

We analyzed four decades of presence–absence data from a fishery-independent survey to characterize the long-term phenology of river herring (alewife, Alosa pseudoharengus; and blueback herring, Alosa aestivalis) spawning migrations in their southern distribution. We used logistic generalized additive models to characterize the average ingress, peak, and egress timing of spawning. In the 2010s, alewife arrived to spawning habitat 16 days earlier and egressed 27 days earlier (peak 12 days earlier) relative to the 1970s. Blueback herring arrived 5 days earlier and egressed 23 days earlier (peak 13 days earlier) in the 2010s relative to the 1980s. The changes in ingress and egress timing have shortened the occurrence in spawning systems by 11 days for alewife over four decades and 18 days for blueback herring over three decades. We found that the rate of vernal warming was faster during 2001–2016 relative to 1973–1988 and is the most parsimonious explanation for changes in spawning phenology. The influence of a shortened spawning season on river herring population dynamics warrants further investigation.

EFFECTS OF THE WATER TEMPERATURE ON TIMING OF SPAWNING AND THE SPAT SETTLING FOR YESSO SCALLOP (MIZUHOPECTEN YESSOENSIS JAY, 1857) IN THE POSYET BAY (PETER THE GREAT BAY, JAPAN SEA)

The water temperature influence on timing of spawning and the spat settling is considered for yesso scallop (Mizuhopecten (=Patinopecten) yessoensis Jay, 1857) in the Minonosok Bay (Posyet Bay, Peter the Great Bay) on the data of observations in 1970–2011. The date of the spawning start varied from May 1 to June 9 (within 40 days) and the start of the scallop spat settling onto collectors of marine farm varied from June 4 to July 5 (within 32 days). Usually the spawning was delayed in the years with long cold season and big sum of daily temperatures below zero or low mean temperature in winter months and April, when the pre-spawning period with the temperature above zero before May 1 was too short. The spat settling was delayed in the years with severe winter or low mean temperature in the pre-spawning period (r = –0.46); the early settling was observed in the years with early warming above 0o C. The higher sum of positive daily temperatures accumulated till May 1 and till June 1, or within April and May, the earlier the spat settling on collectors (r = –0.58; –0.60; –0.55; –0.42, respectively). Prognostic equations for 10-day and 15-day forecasting of the dates of scallop spawning start and spat settling start are proposed and tested; accuracy of these forecasts is 70% for the spawning and 60 % for the spat settling.

MORPHOFUNCTIONAL CHARACTERISTICS OF GONAD OF THE GABLE-ROLL NEOGOBIUS MELANOSTOMUS (PALLAS, 1814) OF THE LOWER NISTRY DURING THE SPAWN

The results of studies of the reproductive system of sexually mature females of the round goby Neogobius melanostomus (Pallas, 1814) from the Lower Dniester during the spawning season are presented. The age of sexual maturation and the timing of spawning of fish in the conditions of this basin are determined. Asynchrony in the development of germ cells has been identified, which provides four-time spawning during the entire breeding season of fish. Throughout the entire reproductive cycle, larger females with greater body weight and gonad mass are the first to spawn.

Environmental factors explain spawning day deviation from full moon in the scleractinian coral Acropora

Broadcast-spawning scleractinian corals annually release their gametes with high levels of synchrony, both within and among species. However, the timing of spawning can vary inter-annually. In particular, the night of spawning relative to the full moon phase can vary considerably among years at some locations. Although multiple environmental factors can affect the night of spawning, their effects have not been quantitatively assessed at the multi-regional level. In this study, we analysed environmental factors that are potentially correlated with spawning day deviation, in relation to the full moon phase, in Acropora corals inhabiting seven reefs in Australia and Japan. We accordingly found that sea surface temperature and wind speed within one to two months prior to the full moon of the spawning month were strongly correlated with spawning day deviations. In addition, solar flux had a weak effect on the night of spawning. These findings indicate that Acropora have the capacity to adjust their development and physiology in response to environmental factors for fine-tuning the timing of synchronous spawning, thereby maximizing reproductive success and post-fertilization survival.