Abstract. The Gulf of California (GC) presents several oceanographic features that make it unique among semienclosed seas of similar latitude and dimensions, the most important being strong tidal mixing, some of it close to deep stratification. Three-dimensional numerical model results suggest that tidal mixing may be more important than the thermohaline circulation in causing the long-term residual circulation, which consists of outflow in the upper 200 m and inflow below, plus a seasonally-reversing surface layer. The GC is an evaporative basin, but in the mean it gains heat through the surface. Lacking a sill at the point of connection with the Pacific Ocean (PO), the GC is constantly shaken by a wide spectrum of signals coming from the PO, including tides, subinertial trapped waves of various frequencies and El Niño. The seasonal dynamics and thermodynamics of the GC are dominated by the PO, not by local wind or buoyancy flux. Local processes are important at shorter time scales and in altering the thermohaline characteristics of the upper-layer waters. Tidal currents generate internal tides, packets of solitons, and sea surface temperature fronts from which jets may form. Coastal upwelling also seems to generate jets that separate from capes, especially on the mainland coast. The mesoscale off-shore circulation in the GC consists of a series of basin-wide geostrophic gyres that reach below 1000 m; their effect on the mean and seasonal circulation and thermodynamics of the GC remains to be studied. During summer, the currents in the mainland continental shelf are due to coastal trapped waves, while during winter they are wind-driven. The most important interannual anomalies in the GC are due to El Niño.

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[1] The mean and seasonal circulation of the Gulf of California is simulated with a threedimensional numerical model, forced by the Pacific Ocean through specifying the sea level, the temperature, and the salinity fields at its entrance. At the sea surface, the wind and the heat and freshwater fluxes are specified. The model reproduces the observed mean and seasonal variability of sea level, of heat and salt balances, and the sea surface temperature (SST) climatology. It also reproduces the general surface circulation of the northern gulf, which consists of a seasonally reversing basin-wide gyre. It is found that tides and heat fluxes are both indispensable to reproduce the spatial structure and temporal evolution of the SST. Tides provide the mixing to upwell the cooler subsurface waters in the large islands area, and the heating from the surface raises the SST. The general circulation of the southern part of the gulf is due to the wind and the Pacific forcing. In the Ekman layer, two periods of anticyclonic circulation and one cyclonic per year occur; below this layer, two cyclonic periods develop. In the northern part, the tides play an important role in producing mean residual currents, and both, tides and winds, compete against the Pacific forcing to produce a cyclonic and anticyclonic circulation once a year. Contrary to conclusions of previous studies, the thermohaline circulation is found to be unimportant in the gulf.

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Marine reserves have been advocated worldwide as conservation and fishery management tools. It is argued that they can protect ecosystems and also benefit fisheries via density-dependent spillover of adults and enhanced larval dispersal into fishing areas. However, while evidence has shown that marine reserves can meet conservation targets, their effects on fisheries are less understood. In particular, the basic question of if and over what temporal and spatial scales reserves can benefit fished populations via larval dispersal remains unanswered. We tested predictions of a larval transport model for a marine reserve network in the Gulf of California, Mexico, via field oceanography and repeated density counts of recently settled juvenile commercial mollusks before and after reserve establishment. We show that local retention of larvae within a reserve network can take place with enhanced, but spatially-explicit, recruitment to local fisheries. Enhancement occurred rapidly (2 yrs), with up to a three-fold increase in density of juveniles found in fished areas at the downstream edge of the reserve network, but other fishing areas within the network were unaffected. These findings were consistent with our model predictions. Our findings underscore the potential benefits of protecting larval sources and show that enhancement in recruitment can be manifested rapidly. However, benefits can be markedly variable within a local seascape. Hence, effects of marine reserve networks, positive or negative, may be overlooked when only focusing on overall responses and not considering finer spatially-explicit responses within a reserve network and its adjacent fishing grounds. Our results therefore call for future research on marine reserves that addresses this variability in order to help frame appropriate scenarios for the spatial management scales of interest.

No-take marine reserves can be powerful management tools, but only if they are well designed and effectively managed. We review how ecological guidelines for improving marine reserve design can be adapted based on an area's unique evolutionary, oceanic, and ecological characteristics in the Gulf of California, Mexico. We provide ecological guidelines to maximize benefits for fisheries management, biodiversity conservation and climate change adaptation. These guidelines include: representing 30% of each major habitat (and multiple examples of each) in marine reserves within each of three biogeographic subregions; protecting critical areas in the life cycle of focal species (spawning and nursery areas) and sites with unique biodiversity; and establishing reserves in areas where local threats can be managed effectively. Given that strong, asymmetric oceanic currents reverse direction twice a year, to maximize 123Rev Fish Biol Fisheries (2018) 28:749-776 https://doi.org/10.1007/s11160-018-9529-y( 0123456789().,-volV) (0123456789().,-volV)

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