Mark A. Morrison

Diurnal and tidal movements of snapper (Pagrus auratus, Sparidae) in an estuarine environment

Using individually coded acoustic transponders and an array of 15 moored receivers (detection range ∼300 m), the temporal and spatial movements of the temperate snapper Pagrus auratus (Sparidae) were studied within an estuary. Of the 28 fish initially tagged, 20 were subsequently detected within the study area for up to 70 days. The spatial scale of daily movements was in the order of hundreds of metres for most fish, suggesting relatively restricted home ranges over the period monitored (November-January). The detectability of fish remaining in the estuary was lower at night, probably because of fish moving out of the main channel and onto surrounding shallow banks during darkness. Temporal movement patterns detected using spectral analyses (Fast Fourier Transforms) were predominantly diurnal, with subordinate tidal behaviour also evident in some fish. These results demonstrate that in this system, snapper occupy relatively small (hundreds of metres) and discrete areas of soft sediment seafloor, within which repeated, predictable movements are made. Variability among fish has highlighted the need for a better understanding of the relationship between fish behaviour and fine-scale habitat features (metres).

Risks of shifting baselines highlighted by anecdotal accounts of New Zealand's snapper (Pagrus auratus) fishery

Abstract Anecdotal data sources may constitute an important component of the information available about an exploited species, as record keeping may not have occurred until after exploitation began. Here, we aimed to fill any gaps in the exploitative history of the sparid snapper (Pagrus auratus), using social and historical research methods. Social research consisted of interviews with recreational fishers, focusing on the most and largest snapper they had caught. In addition, the diary‐logs of two recreational fishers were analysed. Historical research consisted of investigation of old books, photos, archives and unpublished sources unconventional to fishery science. Interviews with fishers demonstrated no or weak trends in snapper abundance or size, and were likely impeded by a lack of ability to detect change in a fish stock that may still be considered abundant. The fishers’ perception of change, however, largely reflected recent experiences (last c. 10 years), when biomass is understood to have increased, and mostly did not consider experiences before the 1980s. Alternatively, diary‐logs of fisher catch rates produced a pattern that matched formal stock assessments of snapper biomass, suggesting declines in abundance up until the 1990s and an increase in biomass after that time. Historical research, although more qualitative, had the ability to investigate periods where formal records were not kept and described a fishery vastly different from the current one. Snapper were easily caught, in great abundance and in unusual locations. Localised depletion of snapper was first noticed in the early 20th century, despite spectacular catches of snapper occurring after that time. Snapper behaviour was also likely different, with visual sightings of snapper by onlookers a common occurrence. Although predictions from stock assessment models are consistent with that of the anecdotes listed here (i.e., high biomass in the past), these anecdotes are valuable as they explain lost biomass in a perspective meaningful to all. This perspective may be valuable for managers trying to consider the non‐financial value of a shared fishery but, if unrecognised, represents a shifting baseline.

Snapper (Chrysophrys auratus): a review of life history and key vulnerabilities in New Zealand

Snapper (Chrysophrys auratus) is an important coastal fish species in New Zealand for a variety of reasons, but the large amount of research conducted on snapper has not been reviewed. Here, we review life history information and potential threats for snapper in New Zealand. We present information on snapper life history, defining stages (eggs and larvae, juvenile and adult), and assess potential threats and knowledge gaps. Overall we identify six key points: 1. post-settlement snapper are highly associated with certain estuarine habitats that are under threat from land-based stressors. This may serve as a bottleneck for snapper populations; 2. the largest knowledge gaps relate to the eggs and larvae. Additional knowledge may help to anticipate the effects of climate change, which will likely have the greatest influence on these early life stages; 3. ocean acidification, from land-based sources and from climate change, may be an important threat to larval snapper; 4. a greater understanding of population connectivity would improve certainty around the sustainability of fishery exploitation; 5. the collateral effects of fishing are likely to be relevant to fishery productivity, ecosystem integrity and enduser value; 6. our understanding of the interrelationships between snapper and other ecosystem components is still deficient.

Invasion of the Asian goby, Acentrogobius pflaumii, into New Zealand, with new locality records of the introduced bridled goby, Arenigobius bifrenatus

Abstract The Asian goby, Acentrogobius pflaumii (Bleeker, 1853), is reported from New Zealand waters for the first time. It was collected by beach seine in 2001–02 from muddy substrata in the upper reaches of the Waitemata and Whangapoua Harbours. We suggest that A. pflaumii has been introduced to New Zealand, probably in ship ballast water. It may have arrived directly from its native range in the north‐west Pacific Ocean, or indirectly via Australia, which it invaded before 1996. The Australian bridled goby, Arenigobius bifrenatus (Kner, 1865), which is also thought to have invaded New Zealand via ballast water, is here recorded from three new locations, extending its known New Zealand range to five different harbours spanning c. 150 km of coastline. This species is more widespread than previously thought and appears well established. Both gobies have been found only on the east coast of the North Island.

Predicting patterns of richness, occurrence and abundance of small fish in New Zealand estuaries

Estuarine fish habitats are vulnerable to human impacts and are poorly studied. We surveyed 69 of New Zealand’s 443 estuaries across 1500 km to: determine species composition of small fishes; model and predict their richness, occurrence and abundance; test marine classification schemes as a basis for Marine Protected Areas; and inform impact mitigation measures. Boosted regression tree models produced acceptable fits for richness and occurrence at estuary and site scales and abundance at the site scale. Richness was greatest in northern North Island; the best predictors were estuary area and area of intertidal habitat. Within estuaries, richness increased towards the head, as water clarity declined and the substratum became muddier. Air temperature, estuary and intertidal area, tidal range and freshwater and seawater influx were the best predictors of occurrence at the estuary scale; water temperature and salinity were important at the site scale. Biological classification schemes seldom improved model fits and have little predictive utility. Richness predictions were made for 380 estuaries and occurrence predictions for 16 species. These predictions inform resource managers about estuarine fishes within their jurisdiction, bypassing the need to undertake expensive field surveys. However, sampling of environmental predictors is still required to drive some models.

Mussel reefs on soft sediments: a severely reduced but important habitat for macroinvertebrates and fishes in New Zealand

Green-lipped mussels (Perna canaliculus) formed extensive reefs on soft sediments in sheltered embayments around northern New Zealand until overfishing and/or increased sediment input caused their virtual disappearance by 1980. To determine the role of mussel reefs as habitat for other animals, we located remnant soft-sediment reefs in five locations and compared the density, biomass, productivity and composition of mobile macroinvertebrate communities, and the density of small fishes associated with mussels, with fauna in the surrounding soft sediments. The mussel reefs had a distinct assemblage of macroinvertebrates, which had 3.5 times the density, 3.4 times the biomass and 3.5 times the productivity of surrounding areas. The density of small fishes was 13.7 times higher than in surrounding areas. These results show that soft-sediment mussel reefs support an abundant and productive fauna, highlighting the probable large loss of productivity associated with the historical decline in mussel habitat and the consequent desirability of restoration efforts.

Variation in morphology and life-history strategy of an exploited sparid fish

Defining appropriate management units to balance productivity and yield of exploited species is fundamental to effective resource management. Anecdotal and tag–recapture information related to morphology, movement behaviour and life-history strategy suggest that separate groups of snapper (Chrysophrys auratus) exist in the Hauraki Gulf, New Zealand. To address the existence of discrete groups, we examined morphology, meristics and otolith chemistry from snapper collected throughout the Hauraki Gulf. We also used tag–recapture information, stable isotope analysis and interpreted functional aspects of morphology and meristics data to understand potential life-history strategy differences. Snapper from rocky reef habitats did not display morphology and meristic features distinct from snapper from soft sediment habitats and differences in otolith chemistry and stable isotope ratios could respectively be explained by a locational influence and predominance of kelp in rocky reef food webs. Conversely, snapper collected from a known spawning area had distinct morphological and meristic features consistent with semi–pelagic sparids and stable isotope analysis also indicated a potentially more pelagic and higher trophic-level diet. Maintenance of population complexity such as this is generally beneficial to fish populations, and can be achieved by revisiting the spatial units used for fishery management.