Pressure indicators

Tourism

The Northern Mexican Pacific has a high tourism demand not only because of its natural beauty but also because of the winter migration of gray and humpback whales. However, tourism can impact cetacean populations mainly by affecting water quality and through collisions and other disturbances caused by whale-watching boats (Burke et al., 2000; GESAMP, 2001; UNEP, 2002; PNUMA, 2003; Robles et al., 2007). Water pollution is mainly caused by the discharge of untreated wastewater from tourism facilities and boats, which release significant amounts of nutrients and pollutants that damage the marine habitat (GESAMP, 2001, 2008; NOAA, 2001; UNEP, 2002). The toxic substances released (including lead or mercury compounds as well as polychlorinated hydrocarbons) can accumulate along the food chain and become stored in the whales’ fat reserves (Lailson-Brito et al., 2008), with negative effects on both their immune system and breeding success (Varanasi et al., 1993; Tilbury et al., 1999; WDCS, 2005; Dolman et al., 2006).

Whale-watching boats disturb the habitat and can sometimes collide with whales, thereby inflicting wounds on them (Constantine, 1999; Urbán et al., 2005; Dolman et al., 2007; Parsons et al., 2007). The indicator Number of whale watching licenses issued indirectly denotes the risk level that these mammals face from tourism activities.

Whale watching is one of the most important ecotourism activities in the northern Mexican Pacific during the winter. The Mexican Ministry of Tourism has listed whale watching among the three most profitable ecotourism activities in the country, contributing about 7.5% to the total economic income of this subsector (Sectur, 2001). Unfortunately, the unregulated growth of this tourism activity can negatively impact whale populations in the short-, medium- and long-term. Its main effects on whale populations are alterations in activity patterns, aberrant social behavior, dietary changes, low breeding success and home-range desertion, among others (Spalding and Blumenfeld in CCA, 2000; INP 2001; Farmer, 2002; Medrano and Urbán, 2002; Lusseau, 2004; Williams et al., 2006; Montero, 2007). The Number of whale watchers can be used as a direct indicator of the pressure imposed by this activity on populations of gray and humpback whales. However, no data are available to document this indicator.

Fishing and tourism ships

Maritime transport, whether for fishing, cargo or passengers, may adversely affect the cetacean populations in a region. Vessels cause indirect impacts by altering water quality, mainly through the discharge of ​​raw wastewater and solid waste into the sea which, in addition to impairing habitat quality, also leads to the incorporation of hazardous chemicals into whale tissues (INP, 2001; Medrano and Urbán, 2002; CCC, 2003; Urban et al., 2005; WDCS, 2005; IPEN-PNUMA, 2007).

Vessel hulls and propellers can directly collide with the animals, inflicting wounds and fractures on or even killing them. Collisions usually occur with tankers, cargo ships, naval and cruise ships (Medrano and Urbán, 2002; Dolman et al., 2006). On the other hand, the sensitivity of marine mammals to engines’ noise also makes them vulnerable to the presence of vessels. Noise can cause behavioral effects, including disruption of feeding, socializing and vocalization periods and changes in diving behavior, and can lead to the displacement of cetaceans from their preferred habitat (Parsons and Dolman, 2004; WDCS, 2004). A prolonged period under noise disturbance can cause stress, weakening and death of animals (Parsons and Dolman, 2004). The Number of fishing vessels and cruise ship arrivals in coastal areas with presence of whales denotes the pressure that shipping imposes on cetacean populations. Currently, only the States on the North Pacific and the Gulf of California coasts have been included in this indicator. Although this indicator has been included in both the FAO’s list of sustainable development indicators and the OECD’s (2008) set of environmental indicators as an indicator of pressure on fisheries, it could also be used to evaluate the pressure on some cetacean species that inhabit or visit the country’s waters.

Fishing

One of the main threats for marine biodiversity is the bycatch by coastal and open ocean fisheries (Fleischer, 1996; PNUMA, 2003; Ross and Isaac, 2004; Soulsbury et al., 2008). It is estimated that, worldwide, more than 300 000 cetaceans (including whales, dolphins and porpoises) are inadvertently killed every year by this activity, which threatens the conservation of many species (Ross and Isaac, 2004). Bycatch of cetaceans occurs in a wide range of fisheries (anchovy, mackerel, herring, tuna and hake, among others), using many different types of fishing gear (e. g., demersal and pelagic trawling and gill nets; Ross and Isaac, 2004), and cause diverse injuries that range from bruises, muscle tears, rips, cuts or fin amputation, to death by asphyxiation (Kuiken et al. in Ross and Isaac, 2004; Rodríguez-Valencia, 2006). The Fish catch in coastal areas with presence of whales indirectly denotes the pressure that fisheries bycatch could impose on cetacean populations inhabiting those waters. Only the States on the North Pacific and the Gulf of California coasts have been included in this indicator. While this indicator has been widely used by international organizations (e. g., ONU, 2007 and OECD, 2008) and by environmental ministries of many countries (e. g., USA and Mexico) to denote the pressure on marine fisheries, here it is used to denote the pressure that these activities impose on marine cetacean populations.