The Tasman and Golden Bays (TBGB) are a semi-enclosed embayment system in New Zealand that supports numerous commercial and recreational activities. We present three ecosystem models of the TBGB ecosystem with varying levels of complexity, aimed at contributing as tools to aid in understanding this ecosystem and its responses to anthropogenic and natural pressures. We describe the process of data compilation through to model validation and analyse the importance of knowledge gaps with respect to model dynamics and results. We compare responses in all three models to historical fishing, and analyse similarities and differences in the dynamics of the three models. We assessed the most complex of the models against initialisation uncertainty and sensitivity to oceanographic variability and found it most sensitive to the latter. We recommend that scenarios relating to ecosystem dynamics of the TBGB ecosystem include sensitivities, especially oceanographic uncertainty, and compare responses across all three models where it is possible to do so.

The Tasman and Golden Bays (TBGB) are a semi-enclosed embayment system in New Zealand that supports numerous commercial and recreational activities.We present three ecosystem models of the TBGB ecosystem with varying levels of complexity, aimed at contributing as tools to aid in understanding this ecosystem and its responses to anthropogenic and natural pressures.We present data compilation through to model validation and analyse knowledge gaps with respect to model dynamics and results.We compare responses in all three models to historical fishing, and analyse similarities and differences in the dynamics of the three models.We assessed the most complex of the models against initialisation uncertainty and sensitivity to oceanographic variability and found it most sensitive to the latter.We recommend that scenarios relating to ecosystem dynamics of the TBGB ecosystem include sensitivities, especially oceanographic uncertainty, and compare responses across all three models where it is possible to do so.

The presence of sperm storage was evaluated in several deep-sea elasmobranchs (Centrophorus squamosus, Centroselachus crepidater, Deania calcea, Brochiraja spinifera, Brochiraja asperula, Apristurus ampliceps, A. exsanguis, A. garricki and A. sinensis), all considered at risk to the impacts of fishing in New Zealand. Biological measurements of reproductive organs (e.g. follicle size and number, oviducal gland size, uterus width and gonad weight) were recorded in addition to conventional macroscopic maturity assessment measures. Histology was conducted on a sample of oviducal glands to investigate the occurrence of sperm storage. Sperm storage was confirmed in three of the nine species: Centroselachus crepidater, Centrophorus squamosus and Brochiraja asperula. To the best of our knowledge, these are the first observations of sperm storage for these genera, and the first in the family Centrophoridae. Sperm storage was observed in macroscopically mature females and also in some females considered macroscopically as maturing. The female reproductive tract may regress substantially between reproductive events to the extent that a mature fish is mis-classified as maturing, and would be consistent with long periods of resting between reproductive events. Alternatively, it is equally possible that aggrieve male mating behaviour results in premature copulation of maturing females. We summarise published occurrences of sperm storage in chondrichthyans, and conclude that sperm storage is most likely ubiquitous in chondrichthyans, and an adaptive benefit to traumatic mating behaviour, that may also be adaptive to low fish densities in the relatively unproductive environment of the deep-sea.

The barnacle Anelasma squalicola is a marine epibiont found on members of the species-rich, deep-sea lantern shark family Etmopteridae (Figure 1A) but is unlike any other epibiotic thoracian barnacles [1]. While many barnacle species are associated with various marine animals including turtles and whales, with the exception of Anelasma these all retain a filter-feeding lifestyle and have a commensal relationship with their host; despite often being deeply embedded in the dermis, no other species has been reported as feeding on its host. Although Anelasma is fully equipped with cirri (thoracic appendages), these are no longer used for filter feeding [1]. Instead, Anelasma embeds a stalk with root-like structures into the flesh of the shark (Figure S1C in Supplemental Information, published with this article online) that it uses to parasitize its host. Here, we show that specimens of Anelasma sampled from all over the world show very little genetic differentiation, suggesting that this innovation coincided with a rapid worldwide expansion.

The reproductive biology of thirteen poorly studied deep-sea elasmobranch species, on Chatham Rise and the Sub-Antarctic region of New Zealand, was assessed. The study species are all commonly caught as bycatch in commercial fisheries and include: three viviparous species (Centroselachus crepidater, Centrophorus squamosus, Deania calcea), five deep-sea catsharks (Apristurus spp.), and five deep-sea batoid species. However, due to a lack of knowledge on their general biology, ecology, and taxonomy – the impact of fishing on these species is unknown. A species’ resilience to fishing pressure depends on its biological productivity and susceptibility to capture. Accurate assessment of maturity is critical to understanding productivity and the effects of fishing pressure on fished stocks. Maturity is commonly assessed macroscopically, using a visual assessment that lacks precision and relies on subjective judgement. The wide array of macroscopic maturity assessment keys, used internationally, employ various sets of characteristics to define the same reproductive processes, which can lead to errors and inconsistencies in maturity assessment and parameter estimates (e.g. length-at-maturity), making direct comparisons between studies difficult. Objective reproductive measurements (oviducal gland size, follicle size, uterus width, follicle number and gonad weight) were used to assess the validity and quality of the macroscopic maturity staging key used in New Zealand, towards determining the onset of maturity and accurately distinguishing between macroscopic stages. The results showed that no single measurement gave a clear-cut indicator of maturity and some fish classified as ‘maturing’ were very likely ‘mature’. Uterus width, follicle size and gonadosomatic index values were found to be the most useful attributes in determining the onset of maturity. Uterus width and follicle size were also useful in determining differences between different macroscopic stages, whilst gonadosomatic index values were useful in distinguishing between reproductive strategies. Histological observations, with a particular focus on sperm storage, were also used to inform the quality of macroscopic maturity assignment. Sperm storage was observed for the first time in Centroselachus crepidater, Centrophorus squamosus and Brochiraja asperula. This study successfully highlighted problems in the macroscopic maturity assessment key currently used in New Zealand and proposes an improved, more objective macroscopic staging key. The improved key aims: 1) to assist in distinguishing between maturity stages, particularly between stage 2 (maturing), stage 2 (resting) and stage 6 (post-partum) females, by examining the same key reproductive structures across all macroscopic stages, and 2) to provide more representative maturity data for use in fisheries and demographic models, for more robust assessment of the impacts of fishing pressure on poorly studied deep-sea chondrichthyans.