Variation in the condition factors of California pelagic fishes and associated environmental factors

Abstract

Time series of condition factors for mackerel, Scomber japonicus, jack mackerel, Truchurus symmetricus, and northern anchovy, Engraulis mordax, stocks in the Southern California region were compared with time series of oceanographic indices to develop hypotheses concerning physical environmental forcing of the population dynamics and energetics of small pelagic fishes. Mackerel and jack mackerel condition factor time series showed decade‐scale variation, whereas those of anchovy showed coherent fluctuations for 1 to 2 years. Mackerel, and to a lesser extent jack mackerel, condition factors were correlated with proxy indices of alongshore advection (sea level), offshore advection (Ekman transport), ambient temperature (shore station temperature), and ambient salinity (shore station salinity). The condition factor of anchovy was much less correlated with environmental variables. Multiple regression analyses which included sea level, upwelling and salinity proxies explained 80% (33%) of the variance in the annual (monthly) condition factor of mackerel. The first‐order variation in condition factors of mackerel and jack mackerel suggests that they are responding to very large‐scale perturbations of the California Current system which are at least partially described by variations in sea level. The population size of mackerel is apparently also responding to these large‐scale perturbations, making it difficult to isolate environmental dependence of condition factors from density dependence. The second‐order variation is more regional in nature and unexpectedly it appears to be associated with upwelling in the Baja California region.

Temporal and geographic variability of sardine maturity at length in the northeastern Atlantic and the western Mediterranean

“…This increased upwelling intensity may have enhanced plankton productivity in the area and hence food availability for sardine and other clupeoid populations. Sardine condition and therefore L 50 may also be partially regulated by density dependence, as observed for other pelagic species (Parrish and Mallicoate, 1995). The fact that the long-term decline in L 50 was inversely related to abundance off southern Galicia, an area that experienced a great decrease in its sardine population during the last two decades (Carrera and Porteiro, 2003), strengthens this possibility.…”

Spatial and temporal density dependence regulates the condition of central Baltic Sea clupeids: compelling evidence using an extensive international acoustic survey

“…In most studies, the density dependence has been shown as negative relation between fish body size and stock abundance of a single species (e.g., herring, Winters and Wheeler 1994;Tanasichuk 1997;Melvin and Stephenson 2007), whereas in the Baltic Proper both sprat and herring condition are linked to the sprat stock, evidencing the occurrence of intra-as well as inter-specific density dependence. The importance of considering the dynamics of potentially competing species in condition studies has also been shown for other species, e.g., mackerel (Scomber japonicus) and jack mackerel (Trachurus symmetricus) in Southern California (Parrish and Mallicoate 1995).…”

Deriving condition indices from standard fisheries databases and evaluating their sensitivity to variation in stored energy reserves

“…Measurements that are highly resolved in space and time pose a considerable logistical challenge; however, many of the existing high-resolution condition databases were developed in support of or by commercial fisheries. For example, industrial sources of information have been used to derive monthly condition indices for pelagic stocks in the Southern California region (Parrish and Mallicoate 1995) and Benguela system (Schülein et al 1995).…”