State of the Bay Report 2010-Final - Anchor Environmental

The average abundance of the four most ubiquitous species in the system over all survey
years was calculated and plotted for each sampling site. In order to investigate changes in the entire
fish community composition between sites and years, multivariate statistical analysis were
conducted using the PRIMER software. Fish density data were fourth-root transformed and the Bay-
Curtis similarity index was used to create similarity matrices. Relationships between sites and years
were represented using multidimensional scaling and these were statistically tested using a one way
or nested (sites nested within years) ANOSIM tests. The principal species contributing to
dissimilarities between years or sites were identified using the SIMPER routine.
10.3 Results
10.3.1 Description of inter annual trends in fish species diversity
At least thirty-six fish species have been recorded in the six seine-net surveys conducted
during 1986-87, 1994, 2005, 2007-2010. This is one less than recorded previously as both sand shark
species, R annulatus and R. blockii were thought to occur in the area and new research indicates that
only the latter species inhabits the Bay and lagoon (Dunn & Schultz in prep.). During recent surveys
three different species of goby of the genus Caffrogobius, namely: C. nudiceps, C. gilchristi and C.
caffer have been identified. Due to the uncertainty surrounding identification of these species in
earlier surveys, they have been grouped at the generic level for data presented in this report. The
species list and abundance of each species caught in Small Bay, Big Bay and the Lagoon during each
of the different surveys are shown in Figure 10.3, Table 10.1 & Table 10.2 respectively. Considering
data from all surveys combined, a similar number of species have been captured in Big Bay (26) and
Small Bay (26) with slightly fewer found in the Lagoon (19) (Figure 10.3, Table 10.1 & Table 10.2).
Species richness was usually highest in Small Bay and varied little over time, although in 2009 & 2010
there was a slight reduction in the number of species caught in Small Bay (Figure 10.2). Little
variation in the number of species caught over the period of sampling is apparent for Langebaan
lagoon and the decrease in the number of species caught in Big Bay between 2008 & 2009 noted in
last year’s report appears more a result of increased diversity in 2008 catches as all the other annual
surveys in Big Bay recorded similar number of species in catches (Figure 10.2).
The actual species composition in the different areas between the five surveys did, however
change substantially (Figure 10.3, Table 10.1 & Table 10.2). Despite the small decrease in species
caught in Small Bay during the 2009 and 2010 sampling surveys, the same nine occurred in all
surveys. For the first time in 2010, the Knysna sand goby was found in hauls made in Small Bay at
both the campsite and Blue Water Bay sites. Five of the 25 species recorded in Big Bay occurred in all
surveys with two more, silversides and elf only absent in one survey each (2007 and 2009
respectively). Similarly, only six of the 19 species found in the lagoon occurred in all surveys. It
appears that Small Bay has the highest proportion of “resident” species that occur there consistently,
whilst a larger proportion of the Big Bay and Langebaan Lagoon ichthyofauna occur seasonally or
sporadically in these areas. This is probably related to the greater temporal variation in
oceanographic conditions in Big Bay and Langebaan Lagoon than in Small Bay and to differences in
habitat type. Short term fluctuations in diversity and abundance of nearshore sandy beach fish
communities with changes in oceanographic conditions are the norm rather than the exception (see
for e.g. Clark 1994). In the earlier surveys (1994-2008), average species richness and abundance (all
species combined) was usually highest in Small Bay and lowest in Big Bay (Figure 10.2, Figure 10.4).
Although this pattern still holds in the 2009 and 2010 surveys, with the average fish density in Small
Bay still double that recorded for Big Bay, similar or greater average abundance was recorded in the
Lagoon samples (Figure 10.4). This was mostly a result of some very large harder catches at two of
the lagoon sites (Schaapen Island and Bottelary) and is simply an indication of the high variability in
surf zone fish densities that will be recorded when shoaling species are part of the fish assemblage
State of the Bay 2010: Saldanha Bay and Langebaan Lagoon 221