Tanga Fisheries Analysis - IUCN

7.2.5. Annual Variations in CPUE for Ngalawa using Jarife
Figure 16 presents a simple graph of mean annual catch-rate by year for the Kigombe data for
ngalawas using jarife (shark net in English though catches are predominantly rays, see section 7.3
below). This graph would seem to indicate a decrease in CPUE between 1996/97 and 1997/98,
with a recovery in 1998/99 which continued through to a peak in 2000/01, dropping again after this.
Figure 16 - Mean Annual CPUE (kg/gr/trip) Ngalawa/Jarife (with 90% Confidence Interval)
Mean Annual Catch Rate (Kg/Gr/Trip)
Ngalawa/Jarife
Mean CPUE (kg/gr/trip)
14
12
10
8
6
4
2
0
Mar 96 -
Feb 97
Mar 97 -
Feb 98
Mar 98 -
Feb 99
Mar 99 -
Feb 00
Mar 00 -
Feb 01
Mar 01 -
Feb 02
Mar 02 -
Feb 03
Mar 03 -
Feb 04
Year
To test the significance of the differences between years, annual mean CPUE data was compared
using the Tukey Test. The results show that the peak in 2000/01 was significantly higher than all
other mean annual catch-rates, and the drop in 1997/98 was significantly lower than all other
years. Data for 2001/02 through 2003/04 are statistically different from that of 1997/98, but are not
different from 1996/97, 1998/99 and 1999/00, suggesting that CPUE in the latest years was similar
to the level recorded in the earlier years.
7.2.6. Seasonal Variations in CPUE for Ngalawas using Jarife
Figure 17 presents monthly CPUE data for ngalawas using jarife. Although not as clear as with
mishipi data, the data do show a similar seasonal trend of increased catch-rates during the
Kaskazi, and notably with distinct peaks around March in 2003 and 2004. Figure 18 presents data
for the period August 2001 to July 2004, using kg/gr/hr as the unit of catch-rate. A degree of
seasonal change in CPUE is suggested but again no strong pattern is apparent. In general data
using gear-numbers for jarife needs to be carefully considered because it appears that the number
of individual nets (often 50m pieces) that make up a single net are not accurately recorded, either
from misunderstanding of the fisher of the question (i.e. they report they use one net), or because
these nets experience considerable wear and particularly tear during use and repairs are frequent.
The precise number and length of each section may therefore not be known by the fishers
themselves.
As observed with mishipi data, the possibly El Niño related decline in CPUE was in 1997/98
indicating what might be a more rapid response to the EL Niño event compared with the madema
fishery. This may reflect some species or even ecosystem effect of El Niño that impacts differently
the species typically caught using mishipi/jarife compared to those species taken by madema.
Again these CPUE data might reflect a change in some other parameter of the fishery, not related
to the El Niño at all.
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