Tanga Fisheries Analysis - IUCN

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7.2. The Spatial and Temporal profile of Fishing Effort and Catch-rate 7.2.1. Annual Variations in CPUE for Ngalawa using Mishipi Figure 10 presents a simple graph of mean annual catch-rate by year (where data are available) for the Kigombe Village data for ngalawas (outrigger canoes) using mishipi (handline). This graph indicates that there has been an increase in CPUE since 1996, although the increase has been slow through 2000 and with the major increase in CPUE occurring in 2003/04. Figure 10 - Mean Annual CPUE (kg/gr/trip) for Ngalawa/Mishipi 1996-2004 from Kigombe village. Error bars represent 90% Confidence Intervals. Mean Annual Catch Rate (Kg/Gr/Trip) Ngalawa/Mishipi Mean CPUE (kg/gr/trip) 4.5 4 3.5 3 2.5 2 1.5 1 0.5 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 In order to test of the significance of this difference a Tukey Test (Kramer Modification) for multiple pair-wise comparisons was conducted. A Bonferroni test was also undertaken. As one might expect, from looking at the graphical representation of the data, 2003/04 data is significantly different (i.e. the CPUE is statistically significantly higher) from that of data from all previous years. And again as one would expect from the graphical presentation, the years 1998/99, 1999/00, 2000/01 and 2001/02 are not significantly different from each other. CPUE data from 2002/03 is significantly lower than all other years. The data presented in Figure 10 aggregates the catch from all species caught by this vessel/gear combination and divides it by the total fishing effort. There are some problems with grouping the data from a multi-species fishery together because it assumes that each of the species that make up the fishery are similar in catchability and/or response to management activities. The average CPUE across the species caught by this gear might therefore hide the fact that some species are making a better recovery than others, or conversely may be in decline. Figure 11 presents data on the catch of changu (emperors [Lethrinidae] and snapper [Lutjanidae]) only using this same vessel/gear combination. This group of species comprises about 40% of the catch-weight of this gear but is the largest single species group contributor to the catch. There are some differences in the catch-rate to be seen compared with the aggregated data, with arguably more of an upward trend in the mean CPUE figures. However, the mean CPUE for 2001/02 is not in fact statistically significantly higher than the preceding year and therefore the apparent trend is not statistically significant. Only 2003-04 is significantly different (higher) from all previously years. 20
Figure 11 - Mean Annual CPUE (kg/gr/trip) for Changu Ngalawa/Mishipi 1996-2004 (with 90% Confidence Intervals) Mean Annual Catch Rate (Kg/Gr/Trip) Ngalawa/Mishipi for Changu Mean CPUE (kg/gr/trip) 4.00 3.50 3.00 2.50 2.00 1.50 1.00 0.50 0.00 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 One is left therefore with a suggestion of a fairly constant, possibly increasing, CPUE (i.e. changu resource abundance) over the duration of the Programme with a sudden increase in CPUE in 2003/04. But it is difficult to say much more than that in terms of the resource of changu as a whole in the areas fished by this selection of fishers from Kigombe Village. Changu, as a group, are not only caught by mishipi and so this analysis can only relate to the species (and particular ages of those species) that comprise the resource of changu that is vulnerable to this particular vessel/gear combination. Because the species in this broad group differ in their ecology and behaviour it is likely that different species of changu will be vulnerable to different vessels/gears and/or at different times of the year. For example, in similar small-scale coastal fisheries in neighbouring Kenya, McClanahan and Mangi (2004) showed that Lethrinus harak comprised about 13% of the catch of gillnet fishers, but a less significant 2-3% of the catch of fish-traps. Lethrinus sanguineus (~28%) and Lethrinus mahsenoides (~27%) on the other hand were the dominant species in the catch of mishipi fishers. So to say that changu have increased in abundance based on the evidence from ngalawa/mishipi may only relate to certain species. Between 1995 and 2001 TCZCDP data only records the single grouping of changu and so it is not possible to differentiate between Lethrinid species over this time series of data in the same way that McClanahan and Mangi were able to with their data. 7.2.2. Seasonal Variations in CPUE for Ngalawas using Mishipi Figure 12 presents monthly CPUE data (with 90% confidence interval) for ngalawas using mishipi to examine seasonal and monthly patterns and to glean other information about the fishery. There is an apparent seasonality indicated by the data, which is particularly obvious in data collected under the 1 st protocol. The CPUE typically has its peak around February-March of each year, coinciding with calmer weather typically associated with North-East Monsoon (Kaskazi) and its lowest values around May-June-July, coinciding with the period of cooler temperatures and higher mean wind speeds associated with the South-East Trade Winds (Kusi). In fact the apparent relationship is on the face of it very strong. There are three immediate candidates, firstly that the local abundance of fish is higher during the warmer period of the Kaskazi due to the reported increase in productivity levels associated with nutrient-rich currents flowing south (Sharp, 1983); secondly, that catch-rates increase because of some change in catchability of the gear, in other words, the fishing gears are more effective at catching fish during this period; or thirdly, the fishing grounds that fishers can reach in the Kaskazi are more productive or have larger fish than those they typically target during the Kusi. A fourth explanation concerns trip length: this is generally probably longer during the Kaskazi than during Kusi (e.g. see Figure 8), and so the observed 21
Page 1 and 2: IUCN Eastern Africa Regional Progra
Page 3 and 4: The designation of geographical ent
Page 5 and 6: 9. References and further reading .
Page 7 and 8: Acknowledgements I would like to th
Page 9: approximately 30% between 1996 and
Page 12 and 13: • The local Central Coordinating
Page 14 and 15: 4. Summary Description of Previous
Page 16 and 17: Mishipi Madema Nyavu RingNet Jarife
Page 18 and 19: Figure 3. Table 8 - Landing Sites S
Page 20 and 21: Table 9 - Comparison of CPUE data f
Page 22 and 23: Figure 4 - Fisheries Data Collectio
Page 24 and 25: the fish levy at the market place.
Page 26 and 27: • Data for spatial analysis over
Page 28 and 29: profile of the sampled data was not
Page 32 and 33: increased catch per trip (per gear)
Page 34 and 35: Figure 13 - Mean CPUE (Kg/Gr/Hr, wi
Page 36 and 37: Figure 15 - Mean CPUE (Kg/Gr/Trip,
Page 38 and 39: Figure 17 - Mean CPUE (Kg/Gr/Trip,
Page 40 and 41: 7.3. Catch Composition The 1 st Pro
Page 42 and 43: Figure 19 - Proportion of Monthly C
Page 44 and 45: 7.4. Variations in Price of Fish by
Page 46 and 47: produced of mean catch per trip aga
Page 48 and 49: Figure 27 - Mean Price against Mean
Page 50 and 51: 7.5. The Use of Different CMAs by L
Page 52 and 53: Figure 28 - Sampled Fishing Activit
Page 54 and 55: Table 19 - Objectives/Result Areas
Page 56 and 57: Table 20 - Summary Table of Results
Page 58 and 59: 8.3.3. Fishing Gear Definitions The
Page 60 and 61: Appendix 1 - Vessel and Fishing Gea

Tanga Fisheries Analysis - IUCN

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