Context Phytoplankton communities in the Southern Ocean are shifting as the region experiences rapid environmental change. Aims To investigate long-term trends or changes in Southern Ocean phytoplankton communities, and model abundance patterns of key dominant genera against sampling year and sea-surface temperature (SST). Methods Using 10 years of Southern Ocean Continuous Plankton Recorder (SO-CPR) data within a 15-year period (2007–21), we examined long-term trends in phytoplankton composition, with emphasis on six ecologically important diatom genera (Chaetoceros, Thalassiothrix, Fragilariopsis, Pseudo-nitzschia, Rhizosolenia and Corethron). Key results Overall diatom and dinoflagellate abundances increased significantly across the sampling domain, whereas the diatom:dinoflagellate ratio remained stable, suggesting little change in the relative contributions of these major phytoplankton groups despite increasing overall abundance. Patterns among focal genera differed, with distinct temporal trends and contrasting relationships with sea-surface temperature, indicating ecological differentiation among dominant Southern Ocean diatoms. Conclusions No single genus accounted for the observed increase in abundance, suggesting a community-wide response to environmental change. Implications These results demonstrated the value of long-term CPR observations for detecting trends, natural variability and ecological change in a rapidly warming Southern Ocean.
Context Fishers report high levels of shark depredation and post-release mortality in the Queensland East Coast Spanish mackerel fishery, yet little empirical data exist for these sources of cryptic mortality, limiting the precision of stock assessments. Aims This research aimed to quantify shark depredation and post-release mortality in this fishery. Methods Depredation rates were recorded across 92 commercial and recreational fishing trips. To estimate post-release survival, 32 Spanish mackerel Scomberomorus commerson were tagged with survival pop-up archival tags. Key results Shark depredation rates were 6% during commercial trips and 36% during recreational trips, with substantial daily variation. Highest depredation occurred in the Lucinda region and lowest in the Far North region. Statistical modelling indicated that sector and latitude had a significant effect on depredation rates, with higher depredation rates for recreational fishing and increasing depredation with more southerly latitude. Post-release survival of S. commerson was 53% and mortality was solely caused by predation shortly after release, likely by sharks. Post-release survival varied regionally, with the highest rates in Sunshine Coast (67%) and lowest in Lucinda (20%). Conclusion Shark depredation and post-release predation lead to substantial extra mortality in the Queensland East Coast Spanish mackerel fishery, particularly in the recreational sector. Implications Shark depredation and post-release survival rates were incorporated into the 2025 stock assessment, improving the precision of fishing mortality assessments and overall stakeholder confidence in the stock assessment outputs. These sources of mortality should continue to be monitored over time. Modifications to fishing practices and adoption of different fishing gears can mitigate depredation.
Context The successful mating of individuals from two genetically differentiated lineages, hybridisation, becomes a concern for conservation when it leads to the loss of distinctive gene pools. Aims Murray cod (Maccullochella peelii) and trout cod (M. macquariensis), two species of conservation concern, were translocated in 1915 into Cataract Reservoir, near Sydney, New South Wales. We assess the extent of hybridisation between these two species in Cataract Reservoir. Methods We obtained nuclear and mitochondrial genotyping data from fish sampled in 2003–06 and 2013. Fish sampled in 2019 and 2025 were genotyped with Diversity Arrays Technology using a double-digest restriction site-associated DNA sequencing (RADseq) approach (DArTseq). Key results We found that first-generation hybrids have trout cod mothers. The current composition of cod in Cataract Reservoir on the basis of DArTseq genotyping of 562 fish is 67% genetically pure Murray cod, 7% genetically pure trout cod, 22% F1 hybrids and <4% other hybrid classes of fish. Conclusions Over 110 years, hybridisation has not led to the loss of genetically intact Murray cod and trout cod in Cataract Reservoir, but the proportion of trout cod appears to be in decline. Implications The risk of species collapse from hybridisation appears low; however, strategies to encourage reproductive isolation between Murray cod and trout cod should be identified.
Context The invasive Lessepsian bivalve Brachidontes pharaonis (P.Fischer, 1870) heavily aggregates on longline mussel farms in the Gulf of İzmir, causing spatial and nutritional competition on the commercially cultivated native mussel Mytilus galloprovincialis. Aims This study evaluated the annual gonad development, gametogenic cycle, and environmental drivers of B. pharaonis to inform management strategies for regional bivalve aquaculture. Methods Monthly sampling was conducted at a commercial longline mussel farm in the Gulf of İzmir between April 2025 and March 2026. Gonad tissues were examined histologically and gonad index (GI) values were correlated with environmental parameters. Key results B. pharaonis exhibited extended reproductive activity throughout the year, peaking in July and September. However, gametogenesis significantly ceased in December, when 90% of the population was in the resting or spent stage. A strong positive correlation was determined between GI values and seawater temperature (r = 0.812; P < 0.01). Female-to-male ratio was 1♀:1.22♂ throughout the study. Conclusions Low winter seawater temperatures limit the reproductive window of B. pharaonis in the northern Mediterranean, resulting in a mandatory winter reproductive resting phase. Implications Shifting mussel spat collector deployment to the December–January period would allow farmers to selectively capture native M. galloprovincialis spats, while effectively avoiding B. pharaonis aggregations.
Context The Atlantic blue crab (Callinectes sapidus) is among the most ecologically and economically damaging invaders in the Mediterranean, and commercial removal is increasingly promoted for population control. Yet, existing gear comparisons often confound pot design with bait, leaving managers without clear guidance on efficient configurations. Aims We tested whether pot design and bait type influence catch per unit effort (CPUE) when their effects are disentangled, and identified the most efficient combination for removal-oriented trapping. Methods Two pot designs (umbrella type, double entrance) were factorially crossed with three baits (chicken, fish, tripe) in standardised trials in Azmak Stream, Türkiye (2023–25). An effort-offset negative binomial model, selected by AIC, yielded estimated marginal means and Tukey-adjusted contrasts. Key results Double-entrance pots achieved 1.54-fold higher CPUE than did umbrella-type pots (95% CI 1.06–2.22). Chicken increased CPUE by 62% relative to fish (IRR = 1.62), whereas tripe reduced it (IRR = 0.38). CPUE peaked in early summer, declining towards autumn. Conclusions Pot design and, especially, bait selection, are decisive operational levers; double-entrance pots baited with chicken were most efficient (~1.49 individuals pot−1 h−1). Implications These standardised benchmarks can optimise control-oriented removals, provided scaled trap use is paired with gear-loss mitigation.
