Depth Refuge and the Impacts of SCUBA Spearfishing on Coral Reef Fishes

In recent decades, spearfishing with SCUBA has emerged as an efficient method for targeting reef fish in deeper waters. However, deeper waters are increasingly recognised as a potential source of refuge that may help sustain fishery resources. We used a combination of historical catch data over a 20-year time period and fishery-independent surveys to investigate the effects of SCUBA spearfishing on coral reef fish populations in the southern Mariana Islands. Two jurisdictions were studied; Guam, where SCUBA spearfishing is practiced, and the nearby Commonwealth of Northern Mariana Islands (CNMI), where SCUBA spearfishing has been banned since 2003. Fishery-independent data were collected using baited remote underwater stereo-video systems (stereo-BRUVs) stratified by depth, marine protected area status and jurisdiction. Herbivores (primary consumers) dominated spearfishing catches, with parrotfish (scarines) and surgeonfish/unicornfish (acanthurids) the main groups harvested. However, the large, endangered humphead wrasse (Cheilinus undulatus) was the main species by weight landed by SCUBA spearfishers. SCUBA spearfishing was associated with declining size of scarines over time and catches shifting from a dominance of large parrotfishes to a mixed assemblage with increasing proportions of acanthurids. Comparisons between Guam and the nearby CNMI revealed differences in the assemblage of fished species and also greater size of scarines and acanthurids in deep water where SCUBA fishing is banned. These results suggest that SCUBA spearfishing impacts reef fish populations and that the restriction of this fishing method will ensure refuge for fish populations in deeper waters. We recommend a ban on SCUBA spearfishing to preserve or aid the recovery of large, functionally important coral reef species and to improve the sustainability of coral reef fisheries.

[1]  Euan S. Harvey,et al.  Influence of Range, Angle of View, Image Resolution and Image Compression on Underwater Stereo-Video Measurements: High-Definition and Broadcast-Resolution Video Cameras Compared , 2010 .

[2]  M. Nyström,et al.  The non-linear relationship between body size and function in parrotfishes , 2008, Coral Reefs.

[3]  R. Gillett.  Monitoring and management of the humphead wrasse 'Cheilinus Undulatus' , 2010 .

[4]  N. Dulvy,et al.  Using informal knowledge to infer human‐induced rarity of a conspicuous reef fish , 2004 .

[5]  Benjamin L. Richards,et al.  The IUCN Red List of Threatened Species: an assessment of coral reef fishes in the US Pacific Islands , 2013, Coral Reefs.

[6]  B. Taylor,et al.  Beyond abundance and biomass: effects of marine protected areas on the demography of a highly exploited reef fish. , 2010 .

[7]  K. Rhodes,et al.  Characterization and management of the commercial sector of the Pohnpei coral reef fishery, Micronesia , 2008, Coral reefs.

[8]  K. Holland,et al.  Bioerosion of coral reefs by two Hawaiian parrotfishes: species, size differences and fishery implications , 2010 .

[9]  Aileen C. Mill,et al.  Size structural change in lightly exploited coral reef fish communities: Evidence for weak indirect effects , 2004 .

[10]  K. Rhodes,et al.  A preliminary market-based analysis of the Pohnpei, Micronesia, grouper (Serranidae: Epinephelinae) fishery reveals unsustainable fishing practices , 2007, Coral Reefs.

[11]  D. Bellwood,et al.  Human activity selectively impacts the ecosystem roles of parrotfishes on coral reefs , 2012, Proceedings of the Royal Society B: Biological Sciences.

[12]  J. Choat,et al.  Comparative demography of commercially important parrotfish species from Micronesia. , 2014, Journal of fish biology.

[13]  M. Kulbicki,et al.  The Humphead Wrasse, Cheilinus Undulatus: Synopsis of a Threatened and Poorly Known Giant Coral Reef Fish , 2003, Reviews in Fish Biology and Fisheries.

[14]  Marti J. Anderson,et al.  CANONICAL ANALYSIS OF PRINCIPAL COORDINATES: A USEFUL METHOD OF CONSTRAINED ORDINATION FOR ECOLOGY , 2003 .

[15]  T. McClanahan,et al.  Perceptions of resource users and managers towards fisheries management options in Kenyan coral reefs , 2005 .

[16]  J. McIlwain,et al.  Observations of migrant exchange and mixing in a coral reef fish metapopulation link scales of marine population connectivity. , 2013, The Journal of heredity.

[17]  T. Pitcher,et al.  Intrinsic vulnerability in the global fish catch , 2007 .

[18]  J. Rizzari,et al.  Effects of Spearfishing on Reef Fish Populations in a Multi-Use Conservation Area , 2012, PloS one.

[19]  A. Kerr,et al.  Marine Reserves and Reproductive Biomass: A Case Study of a Heavily Targeted Reef Fish , 2012, PloS one.

[20]  T. Pitcher,et al.  Fishing down the deep , 2006 .

[21]  V. Paul,et al.  Aspects of Biology and Ecological Functioning of Coral Reefs in Guam and the Commonwealth of the Northern Mariana Islands , 2008 .

[22]  Daniel Pauly,et al.  Re-estimation of small-scale fishery catches for U.S. flag-associated island areas in the western Pacific: the last 50 years , 2007 .

[23]  K. R. Clarke,et al.  Non‐parametric multivariate analyses of changes in community structure , 1993 .

[24]  P. Dayton,et al.  The importance in fishery management of leaving the big ones. , 2005, Trends in ecology & evolution.

[25]  R. Myers.  Guam's Small-Boat-based Fisheries , 1993 .

[26]  A. Bauman,et al.  The state of coral reef ecosystems of Palau , 2005 .

[27]  P. Bongaerts,et al.  The role of deep reefs in shallow reef recovery: an assessment of vertical connectivity in a brooding coral from west and east Australia , 2011, Molecular ecology.

[28]  B. Halpern,et al.  Biological Effects Within No-Take Marine Reserves: A global Synthesis , 2009 .

[29]  B. Riegl,et al.  Coral reefs of the USA , 2008 .

[30]  D. Burkepile,et al.  Herbivore species richness and feeding complementarity affect community structure and function on a coral reef , 2008, Proceedings of the National Academy of Sciences.

[31]  S. Wilson,et al.  Gear-based fisheries management as a potential adaptive response to climate change and coral mortality , 2009 .

[32]  Y. Golbuu,et al.  Changes in the spear fishery of herbivores associated with closed grouper season in Palau, Micronesia , 2014 .

[33]  R. Steneck,et al.  Empirical relationships among resilience indicators on Micronesian reefs , 2012, Coral Reefs.

[34]  Raymond N. Gorley,et al.  PERMANOVA+ for PRIMER. Guide to software and statistical methods , 2008 .

[35]  Euan S. Harvey,et al.  Potential of video techniques to monitor diversity, abundance and size of fish in studies of Marine Protected Areas , 2003 .

[36]  Alison Green,et al.  Monitoring coral reef marine protected areas, version 1 : a practical guide on how monitoring can support effective management of MPAs , 2003 .

[37]  G. Shedrawi,et al.  Cost-efficient sampling of fish assemblages: comparison of baited video stations and diver video transects , 2010 .

[38]  John G. Field,et al.  Using size-based indicators to evaluate the ecosystem effects of fishing , 2005 .

[39]  Yi Liu,et al.  The economic value of Guam’s coral reefs , 2007 .

[40]  M Aaron MacNeil,et al.  Toward pristine biomass: reef fish recovery in coral reef marine protected areas in Kenya. , 2007, Ecological applications : a publication of the Ecological Society of America.

[41]  Marti J. Anderson,et al.  Distance‐Based Tests for Homogeneity of Multivariate Dispersions , 2006, Biometrics.

[42]  P. Bongaerts,et al.  Assessing the ‘deep reef refugia’ hypothesis: focus on Caribbean reefs , 2010, Coral Reefs.

[43]  D. Minton,et al.  The State of Coral Reef Ecosystems of Guam , 2005 .

[44]  S. Sandin,et al.  Trophic Classifications of Reef Fishes from the Tropical U.S. Pacific (Version 1.0) , 2010 .

[45]  B. Riegl,et al.  Coral Reefs of the World , 2008 .

[46]  D. Bellwood,et al.  Limited functional redundancy in high diversity systems: resilience and ecosystem function on coral reefs , 2003 .

[47]  Euan S. Harvey,et al.  Calibration stability of an underwater stereo-video system : Implications for measurement accuracy and precision , 1998 .

[48]  E. Harvey,et al.  Bait attraction affects the performance of remote underwater video stations in assessment of demersal fish community structure , 2007 .

[49]  R. J. Hamilton,et al.  Fishing in the dark-local knowledge, night spearfishing and spawning aggregations in the Western Solomon Islands , 2012 .

[50]  K. Rhodes,et al.  Commercial coral-reef fisheries across Micronesia: A need for improving management , 2011, Coral Reefs.

[51]  A. Manica,et al.  Evidence for a depth refuge effect in artisanal coral reef fisheries , 2009 .

[52]  O. Kinne,et al.  Marine ecology progress series , 1989 .

[53]  Terry P. Hughes,et al.  Call to protect all coral reefs , 2013 .

[54]  J. Savidge.  Guam: Paradise lost for wildlife , 1984 .

[55]  M. D. Stokes,et al.  Connectivity and stability of mesophotic coral reefs , 2011 .

[56]  B. Carroll,et al.  Trends in Reef Fish Population and Associated Fishery after Three Millennia of Resource Utilization and a Century of Socio-Economic Changes in American Samoa , 2009 .

[57]  T. McClanahan,et al.  A framework for adaptive gear and ecosystem‐based management in the artisanal coral reef fishery of Papua New Guinea , 2008 .

[58]  M. Priest,et al.  Evidence of stable genetic structure across a remote island archipelago through self-recruitment in a widely dispersed coral reef fish , 2012, Ecology and evolution.

[59]  Benjamin L. Richards,et al.  Environmental Factors Affecting Large-Bodied Coral Reef Fish Assemblages in the Mariana Archipelago , 2012, PloS one.

[60]  Robin Coleman,et al.  Fishing down a Caribbean food web relaxes trophic cascades , 2012 .

[61]  E. Harvey,et al.  Evidence of artisanal fishing impacts and depth refuge in assemblages of Fijian reef fish , 2011, Coral Reefs.

[62]  J. Castilla,et al.  Spearfishing to depletion: evidence from temperate reef fishes in Chile. , 2010, Ecological applications : a publication of the Ecological Society of America.

[63]  M. Shortis,et al.  Estimation of reef fish length by divers and by stereo-video A first comparison of the accuracy and precision in the field on living fish under operational conditions , 2002 .

[64]  Garry R. Russ,et al.  Decadal-scale rebuilding of predator biomass in Philippine marine reserves , 2010, Oecologia.

[65]  Y. Sadovy,et al.  Reef Fish Spawning Aggregations: Biology, Research and Management , 2012, Fish & Fisheries Series.

[66]  E. Harvey,et al.  Habitat Specialization in Tropical Continental Shelf Demersal Fish Assemblages , 2012, PloS one.

[67]  P. Mumby,et al.  Ecological risk and the exploitation of herbivorous reef fish across Micronesia , 2013 .

[68]  J. Lloret,et al.  Spearfishing pressure on fish communities in rocky coastal habitats in a Mediterranean marine protected area , 2008 .

[69]  N. Polunin,et al.  COASTAL FISHERIES IN THE PACIFIC ISLANDS , 1996 .

[70]  Y. S. D. Mitcheson,et al.  Species Case Studies , 2012 .

[71]  D. Bellwood,et al.  Limited Functional Redundancy in a High Diversity System: Single Species Dominates Key Ecological Process on Coral Reefs , 2009, Ecosystems.

[72]  Patrick Christie,et al.  Assessing the feasibility of ecosystem-based fisheries management in tropical contexts , 2007 .

[73]  P. Legendre,et al.  Shifting dominance among Scarid species on reefs representing a gradient of fishing pressure , 2008 .

[74]  Timothy S. Sherwood,et al.  An Overview of Guam's Inshore Fisheries , 1993 .