Reproductive biology of male common dolphins (Delphinus delphis) in New Zealand waters

Reproductive parameters were assessed in 64 male common dolphins (Delphinus delphis) examined post-mortem from strandings and bycatch in New Zealand between 1999 and 2020. The stages of male sexual maturation were assessed using morphological measurements and histological examination of testicular tissue. Age was determined via growth layer groups (GLGs) in teeth. The average age (ASM) and length (LSM) at attainment of sexual maturity were estimated to be 8.8 years and 198.3 cm, respectively. Individual variation in ASM (7.5-10 years) and LSM (190-220 cm) was observed in New Zealand common dolphins. However, on average, sexual maturity was attained at a similar length but at a marginally younger age (< 1 year) in New Zealand compared to populations in the Northern Hemisphere. All testicular variables proved better predictors of sexual maturity compared to demographic variables (age and total body length), with combined testes weight the best outright predictor of sexual maturity. Reproductive seasonality was observed in male common dolphins, with a significant increase in combined testes weight in austral summer. This aligns with most other studied populations, where seasonality in reproduction is typically observed. Given the known anthropogenic impacts on New Zealand common dolphins, we recommend that these findings be used as a baseline from which to monitor population-level changes as part of conservation management efforts.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00227-023-04266-5.

Knowing the fishery to know the bycatch: bias-corrected estimates of harbour porpoise bycatch in gillnet fisheries

Incidental captures (bycatch) remain a key global conservation threat for cetaceans. Bycatch of harbour porpoise Phocoena phocoena in set gillnets is routinely monitored in European Union fisheries, but generally relies on data collected at low spatio-temporal resolution or over short periods. In Denmark, a long-term monitoring programme started in 2010 using electronic monitoring to collect data on porpoise bycatch and gillnet fishing effort at a fine spatial and temporal scale, including time and position of each fishing operation, together with every associated bycatch event. We used these observations to model bycatch rates, given the operational and ecological characteristics of each haul observed in Danish waters. Data on fishing effort from the Danish and Swedish gillnet fleets were collected to predict fleet-wide porpoise bycatch in gillnets at regional level. Between 2010 and 2020, yearly total bycatch averaged 2088 animals (95% Cl: 667-6798). For the Western Baltic assessment unit, bycatch levels were above sustainability thresholds. These results demonstrate that fishing characteristics are key determinants of porpoise bycatch and that classical approaches ignoring these features would produce biased estimates. It emphasizes the need for efficient and informative monitoring methods to understand possible conservation impacts of marine mammal bycatch and to implement tailored mitigation techniques.

Breeding stage impacts on chronic stress and physiological condition in northern gannets (Morus bassanus)

Physiological condition can affect survival and reproductive success in seabirds. However, seabirds rarely show outward signs of poor physiological condition, making it difficult to identify and address issues before they result in population level impacts. We investigate physiological condition of breeding northern gannets (Morus bassanus) between years and nesting stages. Blood smears were used to quantify blood cell profiles indicative of chronic stress, infection, disease, and immunocompetence. No blood parasites were observed, but elevated Heterophil to Lymphocyte (H:L) ratios, eosinophils, and monocytes suggest higher prevalence of infection in some years. Chronic stress levels, indicated by high H:L ratio, were elevated in incubation and early chick-rearing compared to late chick-rearing, which coincided with poorer body condition in breeding birds. This study highlights the value of haematology as a tool for identifying changing patterns of health that may serve as an early indicator of breeding failure, overwintering mortality, and population declines.

Reproductive biology of female common dolphins (Delphinus delphis) in New Zealand waters

Reproductive biology was assessed in 106 female common dolphins (Delphinus delphis) examined post-mortem from stranding and bycatch events along the New Zealand coastline between 1997 and 2019. The average age (ASM) and length (LSM) at sexual maturity was estimated at 7.5 years and 183.5 cm, respectively. The total number of corpora in mature individuals increased with age and appeared to persist throughout life. Ovarian asymmetry was apparent, with the left ovary displaying higher rates of ovulation, and a maximum of 19 corpora recorded for a 24-year-old female. The estimated ovulation and annual pregnancy rates for mature females were 0.39 year^-1 and 30%, respectively. Conception and calving occurred year-round, with a weak seasonal increase observed in late austral spring and early austral summer. As these data did not clearly show whether seasonality was present, the gestation, lactation, and resting periods were calculated as either 12.6 or 12.8 months based on the presence/absence of seasonality, respectively. Similarly, calving interval ranged from 3.15 to 3.2 years, depending upon whether seasonality was considered. The estimated LSM of the New Zealand population aligns with other populations globally, although the estimated ASM is younger by approximately 6 months. Other reproductive parameters align with Northern Hemisphere populations, although demonstrate variation, which may reflect adaptations to local conditions such as water temperature and prey availability. As the species is subject to anthropogenic impacts including pollution and bycatch, we suggest our findings be used as a baseline with which to monitor trends in population parameters.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s00227-022-04139-3.

Locally-Procured Fish Is Essential in School Feeding Programmes in Sub-Saharan Africa

Fish make an important contribution to micronutrient intake, long-chained polyunsaturated omega-3 fatty acids (n-3 LC-PUFAS), and animal protein, as well as ensuring food and nutrition security and livelihoods for fishing communities. Micronutrient deficiencies are persistent in sub-Saharan Africa (SSA), contributing to public health issues not only in the first 1000 days but throughout adolescence and into adulthood. School feeding programs (SFPs) and home-grown school feeding programs (HGSF), which source foods from local producers, particularly fisherfolk, offer an entry point for encouraging healthy diets and delivering essential macro- and micronutrients to schoolchildren, which are important for the continued cognitive development of children and adolescents and can contribute to the realization of sustainable development goals (SDGs) 1, 2, 3, 5, and 14. The importance of HGSF for poverty alleviation (SDG1) and zero hunger (SDG 2) have been recognized by the United Nations Hunger Task Force and the African Union Development Agency-New Partnership for African Development (AUDA-NEPAD), which formulated a strategy for HGSF to improve nutrition for the growing youth population across Africa. A scoping review was conducted to understand the lessons learned from SFPs, which included fish and fish products from small-scale producers, identifying the challenges and best practices for the inclusion of fish, opportunities for improvements across the supply chain, and gaps in nutritional requirements for schoolchildren which could be improved through the inclusion of fish. Challenges to the inclusion fish in SFPs include food safety, supply and access to raw materials, organizational capacity, and cost, while good practices include the engagement of various stakeholders in creating and testing fish products, and repurposing fisheries by-products or using underutilized species to ensure cost-effective solutions. This study builds evidence of the inclusion of nutritious fish and fish products in SFPs, highlighting the need to replicate and scale good practices to ensure sustainable, community-centred, and demand-driven solutions for alleviating poverty, malnutrition, and contributing to greater health and wellbeing in adolescence.

Impact of the the COVID-19 pandemic on a queen conch (Aliger gigas) fishery in The Bahamas

The onset of the coronavirus (COVID-19) pandemic in early 2020 led to a dramatic rise in unemployment and fears about food-security throughout the Caribbean region. Subsistence fisheries were one of the few activities permitted during emergency lockdown in The Bahamas, leading many to turn to the sea for food. Detailed monitoring of a small-scale subsistence fishery for queen conch was undertaken during the implementation of coronavirus emergency control measures over a period of twelve weeks. Weekly landings data showed a surge in fishing during the first three weeks where landings were 3.4 times higher than subsequent weeks. Overall 90% of the catch was below the minimum legal-size threshold and individual yield declined by 22% during the lockdown period. This study highlights the role of small-scale fisheries as a ‘natural insurance’ against socio-economic shocks and a source of resilience for small island communities at times of crisis. It also underscores the risks to food security and long-term sustainability of fishery stocks posed by overexploitation of natural resources.