Ecology of fishes in Upper Newport Bay, California: seasonal dynamics and community structure

A total of 366 bimonthly (January 1978-January 1979) samples taken with six types of gear (otter trawl, gill net, bag seine, small seine, drop net, square enclosure - allwith replication except the gill net) at four stations inupper Newport Bay, California yielded 51,816 fishes belonging to 46 species and weighing over 353 kg. Atherinops affinis (topsmelt) was the most abundant species accounting for 76% of total individuals. Seven species, all of low trophic levels, made up over 97% of the total catch. Mugil cephalus (striped mullet) ranked first in biomass (= 36% of the total) with six species accounting for more than 80% of the total biomass. The largest number of individuals (71%) was collected with the bag seine, the greatest number of species (35) was captured with the otter trawl and the largest percentage of the biomass (56%)was obtained with the gill net. Species richness, number of individuals and biomass were lowest in January (1978 or 1979) or March and highest in July (numbers, biomass) or September (species). Bimonthly diversity (H') values ranged from 0.48 to 2.17 (overall value 1.05) and tended to be inversely related to abundance levels. Species richness was greatest at Station 4 (the lowermost station) and least at Station 1 (the uppermost station). Numbers of individuals and biomass peaked at Station 2 and reached lowest levels at Station 1.Length-frequency analysis of six of the most abundantspecies indicated utilization of the upper bay by two ormore stages in the life history of these species.More than 92,000 eggs belonging to seven taxa and anunknown category and 426 larvae from 20 taxa were collectedwith a 0.5 m net mounted on an epibenthic sled during thesame bimonthly periods and at the same stations as thejuvenile/adult samples. Most of the eggs were collected atStation 2 in May with the numbers overwhelmingly dominatedby those of Anchoa compressa (deepbody anchovy) (99.7% oftotal numbers). The most abundant larva was that ofClevelandia ios (arrow goby). Nearly 60% of the totallarval catch was made up of members of the family Gobiidae.Larval taxa and individuals were fewest in January (1978).The number of taxa was highest in March, September andJanuary (1979) whereas larval numbers peaked in May. Thenumber of taxa and of individual larvae varied only slightlyamong the four stations.Asymptotic species accumulation curves indicated adequate sampling of juvenile/adult fishes. Cluster analysisproduced eight species groups of resident and periodicspecies that variously utilize the three main habitats(channel, inshore, pannes) in the upper bay. Speciesrichness and abundance were positively correlated with bothtemperature and salinity. Temperature, salinity and depthof capture were frequently correlated with individual species abundances and were used in combination to partially explain the spatial utilization of species and species groups.The upper bay fish community is important and worthy ofpreservation for at least three reasons: 1) it containsspecies assemblages not duplicated in any other coastalenvironment; 2) it contains life history stages of avariety of coastal fish species; and 3) it contains largepopulations of small, low-trophic level species and juveniles of other species which serve as forage for larger, predatory species that are frequently of economic importance. Members of the fish community respond noticeably to altered environmental conditions such as the heavy rainfall (and accompanying low salinity and high turbidity) that occurred during the early months of 1978. The short and long term, as yet often unpredictable, fluctuations in the populations emphasize the need for periodic monitoring and for the development of a mathematical model of the fish community if it is to be thoroughly understood and properly managed. (102pp.)