State of the Bay Report 2011-Final.pdf - Anchor Environmental

State of Saldanha Bay & Langebaan Lagoon 2011
Fish
9 FISH COMMUNITY COMPOSITION AND ABUNDANCE
9.1 Introduction
The waters of Saldanha Bay and Langebaan Lagoon support an abundant and diverse fish fauna.
Commercial exploitation of the fish within the Bay and lagoon began in the 1600’s by which time the
Dutch colonists had established beach-seine fishing operations in the region (Poggenpoel 1996).
These fishers’ targeted harders Liza richardsonii and other shoaling species such as white steenbras
Lithognathus lithognathus and white stumpnose Rhabdosargus globiceps, with much of the catch
dried and salted for supply to the Dutch East India Company boats, troops and slaves at the Castle in
Cape Town (Griffiths et al. 2004). Commercial netfishing continues in the area today, and although
beach-seines are no longer used, gill-net permits holders targeting harders landed an estimated 590
tons valued at approximately R1.8 million during 1998-1999 (Hutchings and Lamberth 2002a).
Species such as white stumpnose, white steenbras, silver kob Argyrosomus inodorus, elf Pomatomus
saltatrix, steentjie Spodyliosoma emarginatum, yellowtail Seriola lalandi and smoothhound shark
Mustelus mustelus support large shore angling, recreational and commercial boat line-fisheries which
contribute significantly to the tourism appeal and regional economy of Saldanha Bay and Langebaan.
In addition to the importance of the area for commercial and recreational fisheries, the sheltered,
nutrient rich and sun warmed waters of the Bay provide a refuge from the cold, rough seas of the
adjacent coast and constitute an important nursery area for the juveniles of many fish species that
are integral to ecosystem functioning.
The importance and long history of fisheries in the Bay and Lagoon, has led to an increasing
number of scientific data on the fish resources and fisheries in the area. Early studies studies, mostly
by students and staff of the University of Cape Town investigated fish remains in archaeological
middens surrounding Langebaan Lagoon (Poggenpoel 1996), whilst many UCT Zoology Department
field camps sampled fish within the lagoon (Unpublished data). Gill net sampling with the aim of
quantifying bycatch in the commercial and illegal gill net fishery was undertaken during 1998-99
(Hutchings and Lamberth 2002b). A once of survey for small cryptic species utilizing rotenone, a fish
specific, biodegradable toxin that prevents the uptake oxygen by small fish, was conducted by
Anchor Environmental Consultants (AEC) during April 2001 (Awad et al. 2003). The data from the
earlier gill netting and rotenone sampling survey was presented in the “State of the Bay 2006” report
(AEC 2006). Seine-net sampling of near-shore, sandy beach fish assemblages was conducted over
short periods during 1986-1987 (UCT Zoology Department, unpublished data), in 1994 (Clark 1997),
and 2007 (AEC, UCT Zoology Department). Monthly seine-net hauls at a number of sites throughout
Saldanha Bay-Langebaan over the period November 2007-November 2008 were also conducted by
UCT M.Sc. student Clement Arendse who was investigating white stumpnose recruitment. These
data were reported on in the “State of the Bay 2008” report (AEC 2009).
Other recent research on the fish fauna of the area includes acoustic tracking and research
on the biology of white stumpnose within Langebaan lagoon and Saldanha Bay, monitoring of
recreational shore and boat angler catches and research on the taxonomy and life history of
steentjies and sand sharks and (Kerwath et al. 2009, Næsje et al. 2008, Tunley et al. 2009, Attwood et
al. 2010). Key findings of these studies include evidence that the Langebaan lagoon MPA effectively
protects white stumpnose during the summer months that coincides with both peak spawning and
peak recreational fishing effort (Kerwath et al. 2009). White stumpnose within the Saldanha-
Langebaan system grow more rapidly and mature earlier than populations elsewhere on the South
African south coast (Attwood et al. 2010). Male white stumpnose in Saldanha Bay reach maturity in
their second year at around 19 cm fork length (FL) and females in their third year at around 22 cm FL
(Attwood et al. 2010). Similar differences in growth rate and the onset of maturity for steentjies
between Saldanha Bay and south coast populations were reported by Tunley et al. (2009). These life
history strategies (relatively rapid growth and early maturity) are probably part of the reason that
stocks of these species have to date been resilient to rapidly increasing recreational fishing pressure
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