Length-Based Assessment of Coral Reef Fish Populations in the Main and Northwestern Hawaiian Islands

Abstract

The coral reef fish community of Hawaii is composed of hundreds of species, supports a multimillion dollar fishing and tourism industry, and is of great cultural importance to the local population. However, a major stock assessment of Hawaiian coral reef fish populations has not yet been conducted. Here we used the robust indicator variable “average length in the exploited phase of the population ()”, estimated from size composition data from commercial fisheries trip reports and fishery-independent diver surveys, to evaluate exploitation rates for 19 Hawaiian reef fishes. By and large, the average lengths obtained from diver surveys agreed well with those from commercial data. We used the estimated exploitation rates coupled with life history parameters synthesized from the literature to parameterize a numerical population model and generate stock sustainability metrics such as spawning potential ratios (SPR). We found good agreement between predicted average lengths in an unfished population (from our population model) and those observed from diver surveys in the largely unexploited Northwestern Hawaiian Islands. Of 19 exploited reef fish species assessed in the main Hawaiian Islands, 9 had SPRs close to or below the 30% overfishing threshold. In general, longer-lived species such as surgeonfishes, the redlip parrotfish (Scarus rubroviolaceus), and the gray snapper (Aprion virescens) had the lowest SPRs, while short-lived species such as goatfishes and jacks, as well as two invasive species (Lutjanus kasmira and Cephalopholis argus), had SPRs above the 30% threshold.

Mesophotic Depth Gradients Impact Reef Fish Assemblage Composition and Functional Group Partitioning in the Main Hawaiian Islands

“…Relative abundance ranked from low (light gray) to high (dark gray, and ordered from shallow water to mesophotic depths along hard-bottom substrate and unconsolidated sampling sites. *Indicate species with spawning potential ratios <30 (Nadon et al, 2015). (B) Proportional relative abundance of functional groups subjected to extractive fishing pressures.…”

“…Higher mesophotic abundances of some groups, and changes in predator communities is a potential indicator of depth refugia (Thresher and Colin, 1986;Bejarano et al, 2014;Andradi-Brown et al, 2016;Lindfield et al, 2016), particularly for the fishery-depleted target species that were more abundant in mesophotic depths (e.g., A. virescens, Caranx ignobilis, Figures 8D, 10), or for redatory species with larger mesophotic body sizes (e.g., C. melampygus, Figure 9C). Given that assessments of MHI reef fish stock exploitation rates and annual catch assignments remain largely constrained to fishery-independent, open-circuit diver depths (i.e., <30 m) or fisheries-dependent, commercial catch/recreational survey data obtained from indeterminate depths (Nadon et al, 2015), the use of BRUVS serves as a promising, shallower compliment to the deep-water camera system (BotCam) utilized for Hawaiian bottom fish stock assessments (Merritt et al, 2011). Finally, additional research parsing depth refugia vs. ontogeny effects in structuring reef fish communities would be beneficial, as largersized mesophotic planktivores ( Figure 9B) could be attributed to ontogenic migrations (Andradi-Brown et al, 2016) and may be less prone to mesophotic predation in lower-complexity habitats that do not provide adequate shelter to more vulnerable size classes.…”

“…Targets species identified as being below a sustainability threshold, i.e., potentially overfished with spawning potential ratio <30%, (Nadon et al, 2015) were additionally flagged within each respective functional group; and b) Hawaiian endemics, i.e., species found solely in the Hawaiian Archipelago and Johnston Atoll (DeMartini and Friedlander, 2004;Randall, 2007;Wagner et al, 2014). Additional details describing group assignments are given in Supplementary Materials, Table S1.…”

Making the transition to co-management governance arrangements in Hawai‘i: a framework for understanding transaction and transformation costs

“…For example, organized fishing interests heckled crowds and decision makers at public meetings, filed petitions to delay an administrative decision, and lobbied new legislators in an attempt to block approval of rules. Respondents frequently reported that organized interests opposed any rules changes despite documented resource depletion across the Hawaiian archipelago (Friedlander and DeMartini 2002;Kittinger et al 2011;Nadon et al 2015). To overcome strategic costs, community members raised public awareness, lobbied legislators, and encouraged citizens to support their proposals.…”

“…Sophisticated tenure arrangements once managed resources for a highly populated and politically complex society in pre-contact times (Beamer and Duarte 2006;Kirch 2010;Beamer 2014;Gonschor and Beamer 2014;. Although marine resources are depleted well below historical levels (Friedlander et al 2014;Nadon et al 2015), fishing and gathering remain socially and culturally significant, while providing an important component of food security for many Hawai'i residents (Vaughan and Vitousek 2013;. Coral reef fisheries depletion in many areas can in part be attributed to a departure from local level, culturally rooted, and place-based regulations to ineffective centralized management.…”