Indirect Effects of Conservation Policies on the Coupled Human-Natural Ecosystem of the Upper Gulf of California

Abstract

High bycatch of non-target species and species of conservation concern often drives the implementation of fisheries policies. However, species- or fishery-specific policies may lead to indirect consequences, positive or negative, for other species or fisheries. We use an Atlantis ecosystem model of the Northern Gulf of California to evaluate the effects of fisheries policies directed at reducing bycatch of vaquita (Phocoena sinus) on other species of conservation concern, priority target species, and metrics of ecosystem function and structure. Vaquita, a Critically Endangered porpoise endemic to the Upper Gulf of California, are frequently entangled by finfish gillnets and shrimp driftnets. We tested five fishery management scenarios, projected over 30 years (2008 to 2038), directed at vaquita conservation. The scenarios consider progressively larger spatial restrictions for finfish gillnets and shrimp driftnets. The most restrictive scenario resulted in the highest biomass of species of conservation concern; the scenario without any conservation measures in place resulted in the lowest. Vaquita experienced the largest population increase of any functional group; their biomass increased 2.7 times relative to initial (2008) levels under the most restrictive spatial closure scenario. Bycatch of sea lions, sea turtles, and totoaba decreased > 80% in shrimp driftnets and at least 20% in finfish gillnet fleets under spatial management. We found indirect effects on species and ecosystem function and structure as a result of vaquita management actions. Biomass and catch of forage fish declined, which could affect lower-trophic level fisheries, while other species such as skates, rays, and sharks increased in both biomass and catch. When comparing across performance metrics, we found that scenarios that increased ecosystem function and structure resulted in lower economic performance indicators, underscoring the need for management actions that consider ecological and economic tradeoffs as part of the integrated management of the Upper Gulf of California.

Untitled

“…However, the results of the simulation indicate a much more optimistic perspective and are consistent with the paper by Valenzuela-Quiñonez et al [35]. Morzaria-Luna et al [50], found that increasing ecosystem function and structure lead to lower economic performance indicators, and joint efforts have been conducted between US and Mexico addressed to outline conservation priorities [51].…”

Reproduction and community structure of fish from winter catch sites from industrial shrimp bycatch from the northeast and southeast Mexican Pacific

“…Tropical shrimp trawl fisheries are often small and have little or no room for bycatch, which means that bycatch is not cost-effective; this is the main reason that bycatch is discarded ( Kelleher, 2004 ). At the global level, on-going trawl design innovations ( Boopendranath et al, 2013 ) have led to greater protection of sea turtles and sea mammals ( Norma Oficial Mexicana, 1996 ; Morzaria-Luna et al, 2013 ; Norma Oficial Mexicana, 2013 ); which, according to the Official Mexican Norm are threatened ( Norma Oficial Mexicana, 2010 ). Still, less charismatic and less economically important species die either during or after trawling ( Hill & Wassenberg, 1990 ; Ramírez-Ramírez et al, 2008 ).…”

“…In addition, the lack of information about the size at first maturity and the reproductive periods, as well as the minimum sizes of catches of less commercially valuable species, have all led to an absence of regulations for small fisheries ( Foster & Vincent, 2010 ; Morzaria-Luna et al, 2013 ). The aim of this work is thus to determine the population structure and relative abundance of the fish species present in shrimp-bycatch from industrial shrimp fishery the northeast and southeast Mexican Pacific, as well as their spatial variability and potential risk involved in the recruitment of the species.…”

Reproduction and community structure of fish from winter shrimp bycatch from the Southeast Gulf of California

“…Nevertheless, there has been a constant emphasis on the impact of this activity on shrimp bycatch fauna; FAO considers this fishery the main source of discards (Kumar and Deepthi, 2006;FAO, 2017). At global level constant proposals and innovations have been made for the design of trawls (Boopendranath et al, 2013), making a great progress in the protection of sea turtles and sea mammals (Morzaria-Luna et al, 2013). However, species considered as minor importance died during the trawling, and these organisms are returned to the sea; leads to environmental contamination (Ramírez-Ramírez et al, 2008).…”

“…In addition to knowing the species of fish that comprise the bycatch, it is important to know their size structure and reproductive status, because a large part of shrimp bycatch organisms correspond to juveniles, or sub adults, which significantly affects recruitment for the following generations (Broadhurst et al, 2000). The lack of information about the size of first maturity, reproductive periods, as well as the minimum sizes of catch, lead an absence of a correct regulation of small fisheries (Morzaria-Luna et al, 2013).…”