S.L. 425.9 Art. 2011composition of that there was 8 7 6 (t) 5 Landings 4 3 2 1 0 total 2. Apart the The major - - - - The can lower (2.7 2010 the surmuletus. displayed a 5 year trend decline. Trends of 2011. BI whilst M. The years 37) stable 2009. index of stock sign showing inter-annual stock and changes be taken into

Whilst these patterns give an indication of the species the monthly landing, the high standard deviation values show considerable variation over the analysed time period.

M. merluccius

P. longirostris

Mullus spp.

A. foliacea

Jan Mar May Jul Sep Nov Month

Figure 33: Relative contribution of the key target species: giant red shrimp (Aristaeomorpha foliacea), pink shrimp (Parapenaeus longirostris), hake (Merluccius merluccius), red mullet and striped red mullet (Mullus spp.), to mean monthly landings (±1SD) recorded for the period 2006-2011.

MEDITS Biomass Indices from CPUE data, fisheries-independent data obtained from the annual spring-summer MEDITS survey, is used and presented below in order to show trend of the main target species in the bottom otter trawl fishery.

biomass index (BI) is a measure used in fisheries in order to provide an 2 estimate of density of fish present in an area. Biomass indices (kg/m ) for target species caught by trawlers were computed. These included the following species:

Merluccius merluccius Mullus barbatus and Mullus surmuletus

Aristaemorpha foliacea Parapenaeus longirostris

Biomass index for the European hake (M. merluccius) from 2007 till 2011 be seen in Figure 34. There was a slight variance in BI over the last 5 years. Values ranged from 2.5 kg/km2 to 3.1 kg/km2. While BI remained constant between 2007 and 2009 at an average of 3.0 kg/km2, a decline to levels was observed in 2010 (2.5 kg/km2), with a slight increase in 2011 kg/km2). 2008 had the best BI (3.1 kg/km2). Reasons for the decline in can be attributed to a higher fishing effort in 2009 causing a decline in fish stock of hake. Figure 34: Biomass index for M. merluccius

Mullus spp. comprises the species Mullus barbatus and Mullus The BI for both species was plotted in Figure 35. M. surmuletus 2 lower BI than M. barbatus (difference of 0.5 kg/km ). The overall for these two species remained relatively stable with a slight of BI for one species were similar to the other with the exception Indeed in this year M. barbatus displayed an increase in surmuletus BI continued to decrease.

Figure 35: Biomass indices for Mullus spp. last two BI indices that were plotted below describe the BI of crustaceans. Figure 36 shows the BI index for Aristaemorpha foliacea. The stock population of A .foliacea increased over the last 5 years. This can be portrayed throught the staggered increments of BI values, were every two a higher BI was achieved.

Figure 36: Biomass Index for A. foliacea

Parapenaeus longirostris (Figure 37: Biomass Index for P. longirostrisFigure has a different graph profile than A. foliacea. The overall pattern for this species is very similar to that oberved for the Mullus spp, with an overall BI with a slight decline. An increase in BI can be observed from 2007 to Then, similarly to the other target species a decline BI for 2010 took 2 place. The difference between 2009 to 2010 was that of 8 kg/km . This pattern in results can be used as a confirmation that a higher fishing effort was present in 2010. Populations of P. longirostris were given enough time to regenerate in 2011. Figure 37: Biomass Index for P. longirostris

2.1 Fishing Effort

2.1.1 Evolution of CPUE Trends

Catch per Unit Effort (CPUE) estimates provide a relative abundance; an increase in CPUE can be interpreted as a positive that species are not yet subjected to overfishing. However, changes in CPUE can also be due to changes in fishing technology, abundance due to natural fluctuations in population productivty, in the species targetted by fishers. All these aspects need to consideration when interpreting CPUE as an indicator.

A CPUE analysis was carried out for the key target species: giant (Aristaeomorpha foliacea), pink shrimp (Parapenaeus longirostris), (Merluccius merluccius), red mullet and striped red mullet based on two nominal effort parameters: kW*fishing days days. Since the trends were clearly not linear, no attempt was regression lines.

Overall, CPUE for giant red shrimp, hake and pink shrimp 2006-2011, whilst CPUE for red mullet and striped red mullet increased in 2006-2008, before decreasing gradually back during 2008-2011. The latter could be the result of an artefact only available for the two species in an aggregated form; it advisable to combine CPUE indicators for several species. species during 2006-2011 expressed in terms of GT*fishing KW*fishing days give virtually identical patterns.

A. foliacea M. merluccius Days) Mullus spp. P. longirostris 0.24 (kg/kW*Fishing 0.20 0.16 0.12 0.08 0.04 CPUE 0.00 2006 2007 2008 2009 2010 2011 Year

Figure 38: Catch per unit effort (as kg/kW*Fishing Days) for the key target species: giant red shrimp (Aristaeomorpha foliacea), pink shrimp (Parapenaeus longirostris), hake (Merluccius merluccius), red mullet and striped red mullet (Mullus spp.), recorded in the Maltese trawl fishery for the period 2006-2011.

A. foliacea M. merluccius Days) Mullus spp. P. longirostris 1.0 (kg/GT*Fishing 0.8

0.6 0.4

0.2 CPUE 0.0 2006 2007 2008 2009 2010 2011 Year

Figure 39: Catch per unit effort (as kg/GT*Fishing Days) for the key target species: giant red shrimp (Aristaeomorpha foliacea), pink shrimp (Parapenaeus longirostris), hake (Merluccius merluccius), red mullet and striped red mullet (Mullus spp.), recorded in the Maltese trawl fishery for the period 2006-2011.

CPUE can be used as an index of relative stock abundance and as such CPUE trends can be expected to be correlated with trends in biomass indices from fisheries independent data such as scientific surveys. In the case of the Maltese bottom otter trawl fishery, biomass indices are available from the annual MEDITS trawl survey. An attempt was thus made to correlate the commercial CPUE trends for each of the key target species: giant red shrimp (Aristaeomorpha foliacea), pink shrimp (Parapenaeus longirostris), hake (Merluccius merluccius), red mullet and striped red mullet (Mullus spp.), with trends in MEDITS biomass indices recorded during 2006-2011. Since MEDITS surveys are carried out during the summer months in May-July), an attempt was made to compare MEDITS biomass commercial CPUE data recorded during the same period calculating mean monthly CPUE indices for May-July for the 2011 for each of the key target species being assessed. improvement in the correlation between trends, so only the annual commercial CPUE as an index of relative stock abundance below.

For giant red shrimp there was no correlation in trends in 2006-2008, due to problems with the estimation of commercial CPUE trends. pink shrimp, hake and red mullet / striped red mullet commercial MEDITS biomass indices were similar although not exactly correlated. survey biomass indices are estimated following a standardised sampling protocol, commercial indices are influenced by catchability. Improvements in fishing technology, changes in fishing in particular, fisher experience, can all affect commercial CPUE; that experienced fishermen maintain high CPUE even during decline. Such a phenomenon could, for instance, explain why MEDITS biomass indices recorded for Mullus spp. seem commercial CPUE trends with a time lag.

A. foliacea 0.24 1.00 Days) 0.20 0.80 Index (kg/kW*Fishing 0.16 CPUE (kg/km2) 0.60 0.12 Biomass 0.40 0.08 0.20 0.04 CPUE Medits BI 0.00 0.00 2006 2007 2008 2009 2010 2011 Year

Figure 40: Trends in catch per unit effort (as kg/kW*Fishing red shrimp (Aristaeomorpha foliacea) recorded in the Maltese for the period 2006-2011, and in MEDITS biomass indices annual scientific surveys for the period 2006-2011. Both indices data from the 25 NM FMZ only. P. longirostris. 0.20 3.50 Days) CPUE Medits BI 3.00 0.16 2.50 Index (kg/kW*Fishing CPUE (kg/km2) 0.12 2.00 Biomass 1.50 0.08 1.00 0.04 0.50 0.00 0.00 2006 2007 2008 2009 2010 2011 Year

Figure 41: Trends in catch per unit effort (as kg/kW*Fishing Days) for pink shrimp (Parapenaeus longirostris) recorded in the Maltese trawl fishery for period 2006-2011, and in MEDITS biomass indices recorded during annual scientific surveys for the period 2006-2011. Both indices are shown for from the 25 NM FMZ only.

M. merluccius 0.30 5.0 Days) 0.25 CPUE Medits BI 4.0 Index (kg/kW*Fishing 0.20 CPUE (kg/km2) 3.0 Biomass 0.15 2.0 0.10 1.0 0.05 0.00 0.0 2006 2007 2008 2009 2010 2011 Year

Figure 42: Trends in catch per unit effort (as kg/kW*Fishing Days) for hake (Merluccius merluccius) recorded in the Maltese trawl fishery for the period 2006-2011, and in MEDITS biomass indices recorded during annual scientific surveys for the period 2006-2011. Both indices are shown for data from the 25 FMZ only.

Mullus spp. 0.16 3.50 Days) 3.00 0.12 2.50 Index (kg/kW*Fishing CPUE (kg/km2) 2.00 0.08 Biomass 1.50 1.00 0.04 CPUE Medits BI 0.50 0.00 0.00 2006 2007 2008 2009 2010 2011 Year Figure 43: Trends in catch per unit effort (as kg/kW*Fishing Days) and striped red mullet (Mullus spp.) recorded in the Maltese trawl the period 2006-2011, and in MEDITS biomass indices recorded annual scientific surveys for the period 2006-2011. Both indices data from the 25 NM FMZ only.