Abstract: Along the East African coast, marine top predators are facing an increasing number of anthropogenic threats which requires the implementation of effective and urgent conservation measures to protect essential habitats. Understanding the role that habitat features play on the marine top predator’ distribution and abundance is a crucial step to evaluate the suitability of an existing Marine Protected Area (MPA), originally designated for the protection of coral reefs. We developed species distribution models (SDM) on the IUCN data deficient Indo-Pacific bottlenose dolphin (Tursiops aduncus) in southern Kenya. We followed a comprehensive ecological modelling approach to study the environmental factors influencing the occurrence and abundance of dolphins while developing SDMs. Through the combination of ensemble prediction maps, we defined recurrent, occasional and unfavourable habitats for the species. Our results showed the influence of dynamic and static predictors on the dolphins’ spatial ecology: dolphins may select shallow areas (5-30 m), close to the reefs (< 500 m) and oceanic fronts (< 10 km) and adjacent to the 100m isobath (< 5 km).We also predicted a significantly higher occurrence and abundance of dolphins within the MPA. Recurrent and occasional habitats were identified on large percentages on the existing MPA (47% and 57% using presence-absence and abundance models respectively). However, the MPA does not adequately encompass all occasional and recurrent areas and within this context, we propose to extend the MPA to incorporate all of them which are likely key habitats for the highly mobile species. The results from this study provide two key conservation and management tools: (i) an integrative habitat modelling approach to predict key marine habitats, and (ii) the first study evaluating the effectiveness of an existing MPA for marine mammals in the Western Indian Ocean.
Abstract: Several studies of marine top predators, above all of seabirds, have
analyzed the effects of either individual age or environmental
fluctuations on reproduction; nevertheless, little is known about the
age patterns in breeding performance in a variable environment.
Photo: Pedro Trejo (c)
investigate the simultaneous influence of age and environmental
conditions on laying dates and egg volumes, we tested different climate
and food availability indices in a transequatorial migratory seabird
using female data from a 23-year study. Our results show an improvement
in breeding parameters with age (i.e., earlier laying dates and greater
egg volumes) but no pattern of senescence in older age groups. The best
models showed an interaction of time and age in breeding performance,
i.e., the age pattern of breeding performance changed each year likely
as a result of environmental variability.
Nevertheless, climatic indexes
used here explained part of that annual variability: NAO and SOI index
accounted for 24 and 20% of deviances in laying dates and egg volume,
respectively. Part of that unexplained variability might be related to
other processes such as intermittent breeding and the individual quality
of breeders, which were not assessed in our study.