Snapper Abundance Research Articles

Integrating multi-disciplinary data sources relating to inshore fisheries management via a Bayesian network

The move towards broader management of marine ecosystems has received significant momentum in recent years. Fundamental to Ecosystem-Based Management (EBM) and Ecosystem-Based Fisheries management (EBFM) is the need to engage relevant stakeholder groups. Here we present a Bayesian network (BN) tool developed to describe the snapper population in the Hauraki Gulf, New Zealand, and investigate possible outcomes of alternative management scenarios on snapper abundance. The Hauraki Gulf is a location where the marine environment is both highly valued and in high demand for the goods and services it provides. Snapper are a key component of this social–ecological system. We developed a BN focussed on key snapper life stages, and the consequences of stressors, including fishing, uses of marine space, land use practises (which influence sediment and nutrient yield), biogenic and environmental habitat variables, and upper level drivers such as climate change, human population growth and the global economy. Parameters were populated through a range of information types, from empirical and model analysis to literature review and expert opinion. Parameters for the core of the BN model (i.e. the snapper life stages and fishing methods) were adjusted so that the predicted effects of fishing reflected those seen in model projections from an age structured population model that had recently been used to inform the management of the snapper population in the Hauraki Gulf. The two most influential factors within this BN were fishing and land–use practises. Although there was a strong impact on snapper populations from land–use practises and resulting sedimentation that detrimentally affects biogenic habitats that juvenile snapper depend on, the potential impact of fishery extraction was much stronger. While fishery extraction of snapper is generally well managed, under the existing management set up it is also the only major stressor that would likely be regulated in response to decreases in the snapper population (regardless of the source of any impact). Engaging stakeholders to address issues such as this remains the greatest challenge facing EBFM/EBM in the Hauraki Gulf, but may be possible with tools such as the BN presented here.

Benthic Structure and Pelagic Food Sources Determine Post-settlement Snapper (Chrysophrys auratus) Abundance

Nursery habitats provide increased survival and growth and are a crucial early life-stage component for many fish and invertebrate populations. The biogenic structures that provide this nursery function, however, are increasingly degraded. Therefore, any effort to conserve, restore or replace habitat with artificial structure should be guided by an understanding of the value provided by that nursery habitat. Here we experimentally manipulated structure across a number of sites by inserting pinnind bivalve mimics into the seabed and deploying video cameras to observe the response of post–settlement stage snapper, Chrysophrys auratus (Forster in Bloch and Schneider 1801). We also collected a range of environmental variables across these sites to determine the relative importance to snapper of benthic vs. pelagic productivity. While the abundance of snapper was low, our results demonstrated a strong association to structure relative to control plots. The environmental variable with the highest correlation to snapper abundance was the abundance of zooplankton eaten by snapper. This result was well supported by the dominance of zooplankton over small benthic invertebrates in snapper gut contents, and the weak influence of benthic infauna in our regression models. These regressions also demonstrated that when combined with zooplankton abundance, turbidity had a negative relationship to snapper abundance. This highlights the importance of relatively clear water in estuaries, which allows post–settlement snapper to more efficiently consume the zooplankton that are present in the water column. The third component that post–settlement snapper require is of course the presence of benthic structure. While benthic habitat structure was the strongest factor affecting juvenile snapper abundance, we did not find any correlations to suggest that this importance was related to energetic sheltering and access to locations with high food flux.

Decadal Changes in the Abundance and Length of Snapper (Chrysophrys auratus) in Subtropical Marine Sanctuaries.

Abundance and length of the highly-targeted snapper Chysophrys auratus were compared between sites in 'no take' areas (Sanctuary Zones: SZ), partial protected areas which are fished (Habitat Protection Zones: HPZ), and areas outside (Outside) the Solitary Islands Marine Park (SIMP), Australia. Baited Remote Underwater Video (BRUV) sampling on shallow rocky reef (15 - 25 m) was conducted annually from 2002 until 2014 in the Austral-winter, covering the decade after these marine park zones were established (2002). Additional deeper sites (25 - 40 m) were sampled in 2010-2011 to assess if findings were more-broadly applicable. Lengths were measured using stereo-BRUVs from 2011-2014. Snapper were significantly more abundant in SZ overall and in most years compared with the other two management types, which did not significantly differ. Snapper rapidly increased after 2 - 3 years protection in all management types, especially SZ. Snapper were present on more SZ deployments than HPZ and Outside after the same period. The positive SZ response in snapper abundance on shallower reef was also found at a broader spatial scale on deeper sites. Again the two fished management types did not show significant differences among each other. There was considerable variation in snapper abundance between years, with strong peaks in 2005, 2009 and 2014 especially in SZ. Abundances remained higher in SZ in the year or two following a strong peak, but decreased to similar abundances to fished areas before the next peak. Snapper length frequency distribution significantly differed between SZ and both fished management types, with more larger snapper within SZ including a higher proportion (58%) that were legal-sized (>25.7 cm FL). HPZ and Outside did not significantly differ from each other, and were dominated by individuals below legal size. Overall, SZ's have positively influenced abundance and length of snapper on these subtropical rocky reefs.

Fishing down a Caribbean food web relaxes trophic cascades

The fishing down of marine food webs has been described in pelagic and demersal sys- tems but rarely documented in coral reef environments. We recorded a rapid shift in fish community structure in Belize that accompanied a marked decline in grouper and snapper abundance and a switch towards smaller, less desirable, herbivorous parrotfishes. In a 6 to 7 yr period (2002-2008/09), observations of large-bodied grouper (Serranidae) declined significantly from an encounter proba- bility of 21% per 200 m 2 transect to just 2%. The biomass of carnivorous snappers (Lutjanidae) underwent a 7-fold decline, primarily in the species Ocyurus chrysurus. During this period, the inclusion of parrotfish in fish catches at nearby Glover's Atoll increased from a frequency of 6% in 2004 to ~20% of speared individuals by 2008. Parrotfish biomass declined by 41% between 2002 and 2008/09, with a major decline in the large and dominant herbivore Sparisoma viride. No changes in parrotfish biomass were detectable in nearby marine reserves during this time. Several important indirect effects of fishing were observed. The biomass of mesopredators including Cephalopholis fulvus, C. cruentatus, and Epinephelus guttatus increased dramatically by 880% as compared to the 2002 levels. We putatively attribute this response to a release from predation and constraints to foraging behaviour imposed by large serranids. Further, we find that the density of adult damselfish of the species Stegastes planifrons and S. partitus decreased by ~45%. We attribute this decline to elevated predation by the increased densities of mesopredators, which have been shown to prey upon juvenile damselfish. No change in damselfish densities was found at 2 con- trol locations where fishing was prohibited. The decline in parrotfish in the central Mesoamerican barrier reef likely accounts for recent anecdotal observations of Halimeda tuna spreading to micro- habitats that have previously been grazed intensively. While these results imply that the resilience of these reefs may be seriously impaired, the Belize Government has recently enacted new legisla- tion to improve the management of grouper and outlaw harvesting of most herbivorous fish.

The use of food resources by 0+ snapper, Chrysophrys auratus, from northern Spencer Gulf, South Australia

Food availability is an important factor in survival and growth of juvenile fish and has been proposed as a major factor shaping the patterns of distribution and abundance of 0+ snapper, Chrysophrys auratus, in New Zealand and Japan. Thus, we tested the hypothesis that diet of 0+ snapper would exhibit spatial variation related to their abundance within a major nursery region. Therefore, we described the stomach contents of 0+ snapper collected from within a nursery region in areas of low and high abundance of 0+ snapper. The data also provided the opportunity to consider sized based differences in diet and temporal feeding patterns. 0+ snapper were generalist carnivores that preyed on a wide range of invertebrates and fish. No evidence of sized based dietary variation was identified but feeding either ceased or was much reduced during the hours of darkness. The major finding was that more polychaetes were present in the stomachs of 0+ snapper in the area of high 0+ snapper abundance than in the areas of low 0+ snapper abundance. The spatial differences in diet observed supports the hypothesis that prey availability is important as a driver of habitat selection by 0+ fish.

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

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.

Estimating the abundance and size structure of an estuarine population of the sparid Pagrus auratus, using a towed camera during nocturnal periods of inactivity, and comparisons with conventional sampling techniques

An estimate of the absolute abundance of a population of the sparid Pagrus auratus (‘snapper’) was obtained by towing a dropped underwater video (DUV) camera close to the sea bed during darkness when this species is inactive (asleep), counting the number of fish present and estimating their sizes. This method was used in an estuary and compared with active (beam trawl, Danish seine, SCUBA visual counts) and passive (multi-panel gillnets, pots, Sabiki jigs, baited underwater video) fish sampling methods. The DUV detected a wide snapper size range (2–70 cm), which from around 5 cm and up appear to represent absolute abundance estimates. For snapper 5 cm and below, density estimates were less than those obtained by fine-mesh beam trawl, which sampled snapper down to 17 mm fork length (recent settlers from the plankton). Total DUV estimates of 0+ snapper abundance (3–9 cm) within this estuarine system were 64,000 ± 20,000 (standard error), compared to 105,000 ± 17,000 by beam trawl. For snapper 10 cm and larger (1+ and older), the DUV population estimate for the harbour was 166,000 ± 28,000. These larger snapper were not vulnerable to the beam trawl, while Danish seine sampling returned estimates of 20,000–80,000 (5000–20,000) fish, depending on the swept area assumptions used. None of the passive methods were able to provide relative or absolute estimates of the overall snapper population size, and each returned strongly skewed snapper length frequencies. The DUV was also able to collect detailed imagery of seafloor habitat features, at the spatial scales of both sampling transects, and individual sleeping fish. This combination of new technologies and specific fish behaviour (sleeping inert on the seafloor) offers a significant new sampling tool for assessing absolute fish abundance and associated population size structures. There is now a strong and ongoing focus by the marine science and management community, on seafloor habitat mapping, and associated Geographic Information System (GIS) resource inventorying. The addition of night deployed DUV sampling into such field deployments offers significant additional fish-habitat information gains to be made within these frameworks, at little additional cost.

Rapid recolonisation of snapper Pagrus auratus: Sparidae within an offshore island marine reserve after implementation of no-take status

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 272:183-190 (2004) - doi:10.3354/meps272183 Rapid recolonisation of snapper Pagrus auratus: Sparidae within an offshore island marine reserve after implementation of no-take status Christopher M. Denny1,*, Trevor J. Willis2, Russell C. Babcock3 1Leigh Marine Laboratory, PO Box 349, Warkworth, New Zealand 2Laboratori Scienze Ambientali, Università di Bologna, Via Saint Alberto 163, 48100 Ravenna, Italy 3CSIRO Marine Research Floreat, Private Bag No. 5, Wembley, Western Australia 6913, Australia *Email: c.denny@auckland.ac.nz ABSTRACT: This study reports the response of snapper Pagrus auratus to the establishment of no-take status in a marine reserve around the Poor Knights Islands in northeastern New Zealand. The Poor Knights and 2 reference locations, Cape Brett and the Mokohinau Islands, were sampled biannually for 4 yr using baited underwater video (BUV). Following the implementation of full marine reserve status at the Poor Knights in October 1998, snapper showed significant increases in abundance and biomass relative to fished control locations. This was particularly apparent for large snapper (>270 mm), whose numbers increased rapidly to levels 7.4 times higher in the final survey compared to the initial pre-reserve survey, and total snapper biomass increased by 818%. There was no significant increase in the abundance, biomass or size of snapper at the reference locations over this time. There was a strong seasonal trend in snapper abundance, with higher numbers in autumn (March/April) compared to spring (September/October). The daily batch fecundity was 11 to 18 times higher at the Poor Knights compared to the reference locations. Once fishing ceased in previously partially protected areas, a rapid recovery of snapper ensued, suggesting that partial fishing regulations are ineffective for protecting targeted species. The speed of increase in snapper density resulted from the immigration of adult fish into the reserve, rather than from within-reserve recruitment. KEY WORDS: Baited underwater video · Poor Knights · Fishing · Partial protection · Temperate reefs · Temporal variation Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 272. Online publication date: May 19, 2004 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2004 Inter-Research.