NOTE Erzini et a!.: Catches in ghost-fishing octopus and fish traps in the northeastern Atlantic Ocean 
323 
= catch in numbers per trap haul; 
- soak time in days; and 
are parameters to be estimated. 
Bridle 
1 00 cm 
Figure 3 
View from the top of a wire fish trap (murejona) showing the 
funnel-shaped entrance. The diameter is 100 cm, the height 35 
cm, and the sides of the triangular wire meshes are approximately 
2.5 cm. 
For each trap type, the Zhou and Shirley 
(1997) model for the relationship between 
catch and soak time for baited traps where 
escapement is possible was fitted by nonlinear 
least squares regression to the catch-per-trap 
data with PROC NLIN software (SAS Insti- 
tute Inc., Cary, NC.) and the equation: 
C(t) = ab + a(t - b)e~ ct , 
where C(t) 
t 
a, b, and c 
For this model, catch is zero at t = 0, the 
asymptotic catch after an infinite soak time 
is the product ab , and maximal catch C max is 
attained at a soak time of f max = 1/c + 6: 
C mnr - ab + ac~ 1 e~ (1+cb> . 
max 
Quantification of trap loss 
Questionnaires were used to survey fishing- 
boat skippers at ten ports of the Algarve, South 
of Portugal. The questionnaires were divided 
between the following areas (area — Barlavento, 
western Algarve and Sotavento, eastern Algarve) and by 
port and fishing vessel (local or coastal). The question- 
naires were designed to quantify the number and type 
of traps used, the number lost per year, reasons for loss, 
and the degree of success in recovery attempts. 
Results 
Catches in deliberately lost traps 
Lost octopus traps caught six species: O. vulgaris, C. 
conger, M. Helena, red scorpionfish ( Scorpaena notata), 
comber ( Serranus cabrilla), and P. phycis. Catch rates 
were generally low and highly variable (Fig. 4). Most 
octopus were captured in the first two weeks after trap 
deployment, and few catches were observed thereafter. 
For other fishes, namely small red scorpionfish, occa- 
sional catches were recorded up to three months after 
deployment. The estimated parameters of the Zhou and 
Shirley (1997) model were a - 3.8576, b = 0.0318, and 
c = 2.292. Based on these parameters the maximal catch 
is attained within 24 hours after deployment (0.47 days), 
and the asymptotic catch rate is 0.12 individuals per trap. 
In addition to all six species caught by the octopus 
traps, fish traps caught damselfish ( Chromis chromis), 
Mediterranean rainbow wrasse (Coris julis), D. annularis, 
D. bellottii, D. vulgaris, S. cantharus, Baillon’s wrasse 
( Symphodus bailloni), and axillary wrasse (S. mediterra- 
neus) and a maximum diversity of 10 species was attained 
27 days after deployment. The most abundantly caught 
species was D. vulgaris that accounted for 43% of the 
fish observed in the traps, followed by D. bellottii (16%). 
Although most of the species were small, some larger 
fish, namely C. conger, were also found in the traps. 
The mean number of individuals per trap peaked 
approximately two weeks after deployment and was 
followed by a sharp decrease from week 4 to 5, and 
then averaged approximately one fish per trap up to the 
end of the three month monitoring period (Fig. 5). The 
estimated maximal catch, based on the parameters of 
the Zhou and Shirley (1997) model (a=1.5397, 6 = 0.5669, 
and c = 0.1101) occurred 9.7 days after deployment, and 
the asymptotic catch rate was 0.87 individuals per trap. 
The same pattern of an initial increase in catches, fol- 
lowed by a decline, was seen in the catches of the most 
abundantly caught species ( D . vulgaris) in individual 
fish traps (Fig. 6). 
The fish trap predator-to-prey ratio, with predators 
considered to be C. conger, O. vulgaris, M. Helena, and 
P. phycis, showed an opposite trend, increasing sharply 
from week 4 to 5 to a maximum of 2.0 35 days after 
deployment, then leveling off (Fig. 5). The initial high 
number of fish observed in the fish traps was largely 
due to the presence of the target species (Sparidae), 
whereas the predators, especially the three fish species 
C. conger, M. Helena, and P. phycis were relatively more 
abundant 55, 71, and 89 days after deployment. 
Whereas the iron frame octopus traps retained their 
structural integrity 12 months after deployment, the 
wire fish traps were completely destroyed. 
Quantification of trap loss 
A total of 84 interviews were conducted, representing 
19.4% of the boats registered in the Algarve (southern 
