Ecology of New Zealand Deep-sea Chondrichthyans

<p>Deep-sea chondrichthyans represent nearly half of the known species of sharks, rays, and chimaeras. Most are poorly known, largely due to their historically low economic value, and thus, low prioritization for research efforts and targeted sampling. Globally, many deep-sea fisheries have proven to be unsustainable, as deep-sea species are generally characterised with life history traits, resulting in low biological productivity. Although generally not targeted, there is a lack of data on New Zealand deep-sea chondrichthyans, despite regularly occurring as bycatch, with no mitigation in place to limit catches. This thesis described aspects of life histories for data deficient deep-sea chondrichthyans caught as bycatch in New Zealand deep-sea fisheries. In Chapter II, research trawl survey data were used to describe and evaluate length-weight relationships, which were found to greatly differ from parameters reported by FishBase. This was followed by the application of a set of models to detect changes in weight at length relationships, and assess if these changes correspond to biological or ecological events, such as length-at-maturity or ontogenetic changes in diet. Chapter III evaluates deep-sea chondrichthyan aggregations and social associations. Not all species were found to engage in aggregative behaviour, but those that did suggested patterns of sex- and size-specific associations which varied with catch density. Adult females were caught most frequently in low densities and were highly associated with other adult females, adult males consistently highly associated with each other, and the highest density catches were dominated by juvenile individuals. These trends may be driven by factors such as foraging, predator avoidance or sexual conflict avoidance. Chapters IV, V, and VI examine, respectively, details of the reproduction, life history, and diet of prickly dogfish (Oxynotus bruniensis), longnose spookfish (Harriotta raleighana) and Pacific spookfish (Rhinochimaera pacifica), and brown chimaera (Chimaera carophila) and black ghost shark (Hydrolagus homonycteris). All species were found to have life histories characteristic of low productivity, including reaching maturation at a large proportion of their maximum length, and having low fecundity. Additional novel biological results included: DNA identification of prey revealed that O. bruniensis preyed exclusively on the egg capsules of holocephalans, potentially making it the only known elasmobranch with a diet reliant solely upon other chondrichthyans; sperm storage was confirmed in female H. raleighana, R. pacifica, and C. carophila; and sexual dimorphism in snout length was found in H. raleighana, where male relative snout size increased at sexual maturity, suggesting that the snout is a secondary sexual characteristic. The depth range of most New Zealand deep-sea chondrichthyans may provide some refuge from current fishing activity. However, results from this thesis have suggested that the species examined here have life histories characteristic of low productivity, and engage in behaviours that will have implications for selective mortality by spatially or temporally stratified fishing. Oxynotus bruniensis, in particular, is likely at higher risk from the impact of fishing than currently estimated, given its reproductive characteristics, highly specialised diet, and distribution overlap with deep-sea fisheries. Continued monitoring and a greater collection of biological data from additional and alternative sources (e.g. fisheries observer program, local fishers, underwater vehicles and video) is recommended to fully understand and negate mortality from human activities.</p>

Ecology of New Zealand Deep-sea Chondrichthyans

<p>Deep-sea chondrichthyans represent nearly half of the known species of sharks, rays, and chimaeras. Most are poorly known, largely due to their historically low economic value, and thus, low prioritization for research efforts and targeted sampling. Globally, many deep-sea fisheries have proven to be unsustainable, as deep-sea species are generally characterised with life history traits, resulting in low biological productivity. Although generally not targeted, there is a lack of data on New Zealand deep-sea chondrichthyans, despite regularly occurring as bycatch, with no mitigation in place to limit catches. This thesis described aspects of life histories for data deficient deep-sea chondrichthyans caught as bycatch in New Zealand deep-sea fisheries. In Chapter II, research trawl survey data were used to describe and evaluate length-weight relationships, which were found to greatly differ from parameters reported by FishBase. This was followed by the application of a set of models to detect changes in weight at length relationships, and assess if these changes correspond to biological or ecological events, such as length-at-maturity or ontogenetic changes in diet. Chapter III evaluates deep-sea chondrichthyan aggregations and social associations. Not all species were found to engage in aggregative behaviour, but those that did suggested patterns of sex- and size-specific associations which varied with catch density. Adult females were caught most frequently in low densities and were highly associated with other adult females, adult males consistently highly associated with each other, and the highest density catches were dominated by juvenile individuals. These trends may be driven by factors such as foraging, predator avoidance or sexual conflict avoidance. Chapters IV, V, and VI examine, respectively, details of the reproduction, life history, and diet of prickly dogfish (Oxynotus bruniensis), longnose spookfish (Harriotta raleighana) and Pacific spookfish (Rhinochimaera pacifica), and brown chimaera (Chimaera carophila) and black ghost shark (Hydrolagus homonycteris). All species were found to have life histories characteristic of low productivity, including reaching maturation at a large proportion of their maximum length, and having low fecundity. Additional novel biological results included: DNA identification of prey revealed that O. bruniensis preyed exclusively on the egg capsules of holocephalans, potentially making it the only known elasmobranch with a diet reliant solely upon other chondrichthyans; sperm storage was confirmed in female H. raleighana, R. pacifica, and C. carophila; and sexual dimorphism in snout length was found in H. raleighana, where male relative snout size increased at sexual maturity, suggesting that the snout is a secondary sexual characteristic. The depth range of most New Zealand deep-sea chondrichthyans may provide some refuge from current fishing activity. However, results from this thesis have suggested that the species examined here have life histories characteristic of low productivity, and engage in behaviours that will have implications for selective mortality by spatially or temporally stratified fishing. Oxynotus bruniensis, in particular, is likely at higher risk from the impact of fishing than currently estimated, given its reproductive characteristics, highly specialised diet, and distribution overlap with deep-sea fisheries. Continued monitoring and a greater collection of biological data from additional and alternative sources (e.g. fisheries observer program, local fishers, underwater vehicles and video) is recommended to fully understand and negate mortality from human activities.</p>

Fish diversity drives regional productivity but not stability in southeastern United States coastal marine fishes

Aim: Ecosystem-based management requires accurate predictions on how biotic and environmental factors interact to deliver ecosystem services. Biodiversity-ecosystem function (BEF) theory predicts that as diversity increases, the ecosystem will become more productive (positive diversity-productivity relationship: DPR) and more stable (positive diversity-stability relationship: DSR). Support for BEF has been primarily derived from fine-grained, non-harvested systems. The purpose of this study is to examine the robustness of BEF predictions for the DPR and DSR by examining how well fish diversity predicts productivity and stability of fish, shrimp, and flounder at a regional scale. Location: Southeast coast of United States. Time Period: 1989 - 2015. Major Taxa Studied: Marine Fishes. Methods: We used 27 years of the SEAMAP-SA Coastal Trawl Survey database to derive estimates of fish, shrimp, and flounder biomass (i.e., productivity), temporal stability of biomass (i.e., invariability of productivity), and fish community species richness. We pooled trawls into 22 km x 22 km raster cells and 3-year time bins. We controlled for variation in sampling effort using sample-based rarefaction. We compared the ability of fish species richness, water salinity, and water temperature to predict biomass and stability of all fish, shrimp, and flounder using multiple linear regression. Results: Both the DPR and DSR exhibited positive log-log linear trends as expected, but the DPR had a much stronger signal. Species richness outperformed the environmental covariates in both the fish and shrimp DPR models. Surface temperature was the most important variable in both flounder models. Overall, our models better explained productivity than stability. Main Conclusions: The DPR and DSR are relevant at regional scales in a commercially important fishery although support for the DSR is less justified than DPR. Further investigation into the underlying mechanisms driving the DPR and DSR are necessary to design management around BEF theory.

Exploring Deep-Sea Biodiversity in the Porcupine Bank (NE Atlantic) through Fish Integrative Taxonomy

This study combined morphological and molecular approaches to the species assignment of several rare or poorly known deep-water fishes caught between 549 and 1371 m depth during a Spanish bottom trawl survey in the Porcupine Bank, west of Ireland. The following fish species were identified: Nessorhamphus ingolfianus (Schmidt, 1912), Borostomias antarcticus (Lönnberg 1905), Scopelosaurus lepidus (Krefft and Maul 1955), Bathypterois dubius Vaillant, 1888, Evermannella balbo (Risso, 1820), Antimora rostrata (Günther, 1878), Melanonus zugmayeri Norman, 1930, Lyconus brachycolus Holt and Byrne, 1906; Paraliparis hystrix Merrett, 1983, Neocyttus helgae (Holt and Byrne, 1908); Platyberyx opalescens Zugmayer, 1911; Howella atlantica Post and Quéro, 1991, Lycodes terraenovae Collett, 1896 and Pseudoscopelus altipinnis Parr, 1933. The presence of L. brachycolus, P. opalescens and P. altipinnis is reported for the first time in the Bank. The DNA barcoding results were largely consistent with morphological identification in 10 species but four did not fit the current taxonomy, indicating cases of potential cryptic speciation, misidentification, synonymy or recent diversification. Among them, the results strongly suggest that P. garmani and P. hystrix are conspecific, making P. hystrix a junior synonym of P. garmani.

​Spatial and Temporal Distribution of Portunus trituberculatus in the Northern East China Sea based on Different Modelling Approaches

Background: Portunus trituberculatus is an important economic crab in the East China Sea. With the increase of tonnage and power of offshore fishing vessels, fishing intensity also increases, which has caused great pressure on P. trituberculatus resources. Protecting P. trituberculatus and achieving sustainable utilisation of resources are urgent problems that need to be solved. Therefore, protection and rational development of P. trituberculatus resources are important to accurately understand its spatial and temporal distribution. Methods: In this study, the temporal and spatial distribution predictive models of P. trituberculatus in the northern East China Sea were built on the basis of three analysis methods (generalised additive model [GAM], random forest [RF] and artificial neural network [ANN]) using bottom trawl survey data and environmental data from 2006 to 2007. The fitting and prediction performances of these three models were compared. Result: Season and sea bottom temperature were the most important factors on the distribution of P. trituberculatus. The fitting performance of ANNs was better than those of GAMs and RFs, but its predictive performance was worse than those of GAMs and RFs. Therefore, RFs was the appropriate model in predicting the distribution of P. trituberculatus in the northern East China Sea. The abundance of P. trituberculatus was significantly higher in summer than in other seasons (P less than 0.01) and generally higher in the northern part of the study area than in the southern part in all seasons.

Confidence Intervals for the Coefficient of Quartile Variation of a Zero-inflated Lognormal Distribution

There are many types of skewed distribution, one of which is the lognormal distribution that is positively skewed and may contain true zero values. The coefficient of quartile variation is a statistical tool used to measure the dispersion of skewed and kurtosis data. The purpose of this study is to establish confidence and credible intervals for the coefficient of quartile variation of a zero-inflated lognormal distribution. The proposed approaches are based on the concepts of the fiducial generalized confidence interval, and the Bayesian method. Coverage probabilities and expected lengths were used to evaluate the performance of the proposed approaches via Monte Carlo simulation. The results of the simulation studies show that the fiducial generalized confidence interval and the Bayesian based on uniform and normal inverse Chi-squared priors were appropriate in terms of the coverage probability and expected length, while the Bayesian approach based on Jeffreys' rule prior can be used as alternatives. In addition, real data based on the red cod density from a trawl survey in New Zealand is used to illustrate the performances of the proposed approaches. Doi: 10.28991/esj-2021-01289 Full Text: PDF