ghana climate change vulnerability and adaptation assessment

The potential impacts of increased temperatures or changes in rainfall as a result of climate change are at thispoint unpredictable for Lake Volta or any other inland fisheries in Ghana. Little up-to-date, quantitative data isapparently available for this important fishery although as noted, some sources indicate the fishery is declining orat risk of decline under current fishing pressure. Continued warming as predicted by current trends and climatemodel projections could, for example, affect primary and secondary productivity in feeder rivers and the reservoir,changing the seasonality, quality, and quantity of the food source of fishes in unknown ways. Warming wouldlikely also affect rates of egg development, fish metabolism and growth, and ultimately recruitment, and perhapseven the timing of reproduction of Lake Volta fishes. Similarly, future climate scenarios resulting in dramaticallydecreased or increased river flows (Kasei, 2009, see Desertification section) would also likely affect the fishery butin less easily conceptualized ways. For example, in the case of reduced flow, lower water levels in Lake Volta andtributaries would reduce the area of shallow, shoreline habitat. In turn, loss of the vegetated shoreline-lakeinterface would affect fishes using such habitats for feeding, spawning, or nursery areas. Depending on timing andvariability, higher flows could change seasonal turbidity (and perhaps primary and secondary productivity) anddilute food resources, resulting in largely unpredictable changes on larvae, juveniles, and adult fishes. Clearly, thecurrent state of the inland fishery resource in Ghana deserves further scientific attention as does the potentialimpacts climate change might have on this resource.CLIMATE CHANGE AND THE MARINE FISHERYThe most prominent effect of climate change on marine productivity and ultimately the fishery could be increasedsea temperatures, even though the primary proximate driver of productivity, the upwelling system, is admittedlycomplex and certainly not totally understood (Wiafe et al., 2008). Changes in sea temperature could affect primary(phytoplankton) and secondary (zooplankton) production which in turn could dramatically increase or decreasethe abundance of pelagic fishes and their predators.Historical trend analyses of sea temperature in the Gulf of Guinea tend to show increasing trends in sea-surfacetemperatures for the period of record in the late 20 th century. Simple regression of annual mean data from about1960-2001 indicated generally low interannual variability and an increased trend, albeit non-significant, in seasurfacetemperature (Dontwi et al., 2008). Another more detailed analysis (covering through 1992) showed: anoverall increase in offshore sea-surface temperature from 1946-1990 with some evidence of short-lived, cyclical,decadal decreases; consistently increasing temperatures during the second warm (or low) season between 1975-1992, generally increasing sub-surface temperature (100 m depth) from 1969-1992, increasing sea-surface and subsurfacetemperatures during the second warm or low season, generally reduced temperatures during the minorupwelling period (i.e., the upwelling was intensified), and slight increases in temperatures during the main warm orlow season (i.e., intensification of warming).The period 1963-1992 could be divided into three distinct periods: an unsettled period from 1963-1974; a “cold”period from 1975-1980; and a “warm” period from 1981-1992. These periods apparently influenced the dynamicsof the pelagic fishery resources with significant changes in the distribution and abundance of species coincidingwith climatic periods (Koranteng and McGlade, 2001). Notably, another detailed analysis of seasonal trends overa 24-year period (1968-1992) showed the annual cyclical nature of temperature and zooplankton productivity butalso revealed gradual increases in sea-surface temperature for the major upwelling and second warm or low season(second thermocline) periods (Waife et al., 2008). Notably, these upward trends in sea-surface temperature wereassociated with significant decreasing trends in zooplankton biomass. Although other factors certainly influencedbiomass of zooplankton (e.g., biomass of and predation by sardinella larvae), increased sea-surface temperaturesaccounted for >50 percent of the variation in zooplankton biomass (Waife et al., 2008). Notably, futureprojections of sea-surface temperature from Global Climate Models estimate a 0.4, 1.4, and 2.7°C increase in seasurfacetemperature in coastal waters of Ghana by 2020, 2050, and 2080, respectively (Minia, 2008).The most abundant pelagic species in the upwelling region of the Gulf of Guinea all are zooplankton dependentat early life stages and some are zooplankton dependent as adults (i.e., round sardinella, Sardinella aurita; Madeiransardinella, S. maderensis; European anchovy’ (Engraulis encrasicolus; in some years, chub mackerel, Scomber japonicas;Mensah and Koranteng, 1988; Koranteng, 1995). Plankton abundance, providing forage for juvenile or adult fish,may be more important for sustaining stock biomass of some species than spawning success and larval survival116 GHANA CLIMATE CHANGE VULNERABILITY AND ADAPTATION ASSESSMENT