Owen F. Anderson

New Zealand Demersal Fish Assemblages

Demersal fish assemblages in the New Zealand Exclusive Economic Zone were identified using presence–absence data from 19 215 bottom trawl tows made over a 37-year period. The dataset spanned latitudes 34–54°S and depths of 4–1500 m. A total of 123 taxa occurred in more than 1% of the tows (121 fish and 2 squid). Multivariate ordination and classification (correspondence analysis and Wards cluster analysis) identified four primary species assemblages that were associated with the inner continental shelf, mid–outer continental shelf and shelf edge, upper continental slope and mid continental slope. The most frequently occurring species (> 40% of tows) in each assemblage were (in descending order): inshore – Chelidonichthys kumu, Pagrus auratus and Zeus faber; shelf – Nototodarus spp., Squalus acanthias and Thyrsites atun; upper slope – Macruronus novaezelandiae, Lepidorhynchus denticulatus, Genypterus blacodes and Hydrolagus sp.; mid slope – Hoplostethus atlanticus, Etmopterus baxteri, Halargyreus johnsonii, Coryphaenoides subserrulatus, Deania calcea, Coryphaenoides serrulatus, Pseudocyttus maculatus, Mora moro, Diastobranchus capensis and Centroscymnus crepidater. Further species associations were also identified within each primary assemblage. Canonical correspondence analysis revealed that most of the explainable variation in species composition was associated with depth and latitude; longitude and season explained little extra variance. The usefulness of our results is limited by the use of presence–absence rather than abundance data, and by the uneven spatial distribution of trawl tows. However, the present study provides a large-scale framework within which to interpret the results of studies using abundance data over smaller spatial and temporal scales.

Analysis of bycatch in the fishery for orange roughy, Hoplostethus atlanticus, on the South Tasman Rise

Government fisheries observers made detailed records of the catch weights of all species caught on 545 trawls between October 1997 and August 2000 in the South Tasman Rise orange roughy (Hoplostethus atlanticus) fishery. Bycatch ratios, the ratio of bycatch weight to tow duration, were derived from these data and used to make estimates of total annual bycatch for several species groups. Bycatch ratios based on tow duration were chosen over ratios based on orange roughy catch weights after comparing the coefficients of variation (c.v.) of sets of trial data. Bycatch ratios and total bycatch were estimated for three species of oreos (Oreosomatidae), corals and all other bycatch species combined, for the fishing years from 1997–1998 to 2000–2001. Total oreo bycatch dropped from about 7400 t to less than 350 t during this time. These estimates agreed well with recorded oreo landings data for three of the four years. There was a considerable bycatch of corals, with both the bycatch ratio and the total bycatch reducing during the period examined, the latter from about 1750 t to 100 t per year. The coral bycatch comprised a large number of species, but was dominated by the reef-forming stony coral Solenosmilia variabilis. Annual bycatch of all other species combined, mainly rattails (Macrouridae) and dogfishes (Squalidae), was low (13–120 t). Bycatch of this group dropped sharply in each year as the result of a combination of decreasing bycatch ratio and decreasing fishing effort.

Multiple techniques for determining stock relationships between orange roughy, Hoplostethus atlanticus, fisheries in the eastern Tasman Sea

Abstract Five techniques were used to determine stock relationships between four spatially isolated but geographically close orange roughy fisheries in the eastern Tasman Sea: the Lord Howe Rise (HOWE), Northwest Challenger (NWCH), Southwest Challenger (SWCH), and Westpac Bank (WPAC). The techniques included life history traits (age and length at maturity), population length frequency analysis, otolith shape analysis, genetic makers, and a comparison of spawning times. The estimated ages and lengths at onset of maturity did not identify clear stock differences between the four areas. Otolith shape revealed two groups: HOWE/NWCH and SWCH/WPAC. There were significant size differences between HOWE and NWCH (and between HOWE–SWCH and HOWE–WPAC) with larger fish on HOWE. One out of six nuclear DNA markers revealed significant heterogeneity among sites. Mitochondrial DNA polymorphisms of the control region revealed no heterogeneity among areas, but restriction digests of the whole mitochondrial genome revealed differences between HOWE and NWCH/SWCH. There was considerable between-year variation in the time of the onset of spawning at SWCH (3 weeks) and WPAC (4 weeks). In both areas, the time of spawning was later in the early 1990s than in the late 1990s. No major oceanographic features that might isolate stocks were identified in this region of the Tasman Sea. The biological differences between orange roughy taken from HOWE, NWCH, and SWCH indicate that these fisheries could be managed as independent stocks. There were no biological differences between SWCH and WPAC and these fisheries probably exploit one straddling stock.

Deep-Sea Fish Distribution Varies between Seamounts: Results from a Seamount Complex off New Zealand

Fish species data from a complex of seamounts off New Zealand termed the “Graveyard Seamount Complex’ were analysed to investigate whether fish species composition varied between seamounts. Five seamount features were included in the study, with summit depths ranging from 748–891 m and elevation from 189–352 m. Measures of fish species dominance, rarity, richness, diversity, and similarity were examined. A number of factors were explored to explain variation in species composition, including latitude, water temperature, summit depth, depth at base, elevation, area, slope, and fishing effort. Depth at base and slope relationships were significant with shallow seamounts having high total species richness, and seamounts with a more gradual slope had high mean species richness. Species similarity was modelled and showed that the explanatory variables were driven primarily by summit depth, as well as by the intensity of fishing effort and elevation. The study showed that fish assemblages on seamounts can vary over very small spatial scales, in the order of several km. However, patterns of species similarity and abundance were inconsistent across the seamounts examined, and these results add to a growing literature suggesting that faunal communities on seamounts may be populated from a broad regional species pool, yet show considerable variation on individual seamounts.

A review of New Zealand and southeast Australian echinothuriinids (Echinodermata: Echinothuriidae) with descriptions of seven new species

Examination of a large collection of echinothurioid echinoids from museum collections in New Zealand and Australia revealed six new species in the genus Araeosoma (A. bidentatum sp. nov., A. migratum sp. nov., A. anatirostrum sp. nov., A. tertii sp. nov., A. leppienae sp. nov., and A. bakeri sp. nov.) and one in the genus Hapalosoma (H. amynina sp. nov.), while the recorded presence of A. coriaceum in northwest New Zealand was found to be incorrect. Several of the species described are rarely collected, their distribution being strongly associated with seamount type habitat in a relatively narrow depth range. The majority of the records of these new species are from the New Zealand region, with a strong centre of diversity revealed among the seamounts of the Bay of Plenty. The new species are clearly distinguished from known forms by characters of their pedicellariae, spines, coronal plate structure, colouring, and tuberculation. A key to the Echinothuriinae of the region is included.

High-Resolution Habitat Suitability Models for the Conservation and Management of Vulnerable Marine Ecosystems on the Louisville Seamount Chain, South Pacific Ocean

Vulnerable marine ecosystems (VMEs) are ecosystems at risk from the effects of fishing or other kinds of disturbance, as determined by the vulnerability of their components (e.g., habitats, communities or species). Habitat suitability modelling is being used increasingly to predict distribution patterns of VME indicator taxa in the deep sea, where data are particularly sparse, and the models are considered useful for marine ecosystem management. The Louisville Seamount Chain is located within the South Pacific Regional Fishery Management Organisation (SPRFMO) Convention Area, and some seamounts are the subject of bottom trawling for orange roughy by the New Zealand fishery. The aim of the present study was to produce high-resolution habitat suitability maps for VME indicator taxa and VME habitat on these seamounts, in order to evaluate the feasibility of designing within-seamount spatial closures to protect VMEs. We used a multi-model habitat suitability mapping approach, based on bathymetric and backscatter data collected by multibeam echo sounder survey, and data collected by towed underwater camera for the stony coral and habitat-forming VME indicator species Solenosmilia variabilis, as well as two taxa indicative of stony coral habitat (Brisingida, Crinoidea). Model performance varied among the different model types used (Boosted Regression Tree, Random Forest, Generalized Additive Models), but abundance-based models consistently out-performed models based on presence-absence data. Uncertainty for ensemble models (combination of all models) was lower overall compared to the other models. Maps resulting from our models showed that suitable habitat for Solenosmilia variabilis is distributed around the summit-slope break of seamounts, and along ridges that extend down the seamount flanks. Only the flat, soft sediment summits are predicted to be unsuitable habitat for this stony coral species. We translated a definition for stony coral-reef habitat into a Solenosmilia variabilis abundance-based threshold in order to use our models to map this VME habitat. These maps showed that coral-reef occurred in small and isolated patches, and that most of the seabed on these seamounts is predicted to be unsuitable habitat for this VME. We discuss the implications of these results for spatial management closures on the Louisville Seamount Chain seamounts and the wider SPRFMO.