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Project background and objectives
In many ways, human use is the focus of the Isla Alcatraz Program.
The vast majority of threats to the island’s flora and fauna
are human in origin; and it is the use of the island by humans that
will be "managed" by any management plans that are implemented.
In the fall of 2000, the center began a study monitoring the human
use of Isla Alcatraz.
Today, the main users
of the Midriff Islands are fishermen,
tourists, and researchers. These forms of use and their impacts
are growing throughout the Gulf of California. The most significant
ecological impacts that today’s human visitors to islands
can have are disturbance of flora and fauna (especially birds) and
the introduction of exotic species. For example, the introduction
of cats and rats to Isla Rasa severely impacted that island’s
populations of nesting seabirds.
Like other Midriff Islands,
Isla Alcatraz has a high density and diversity of nesting seabirds
and wading birds. However, the island is particularly susceptible
to all forms of human impact due to its proximity to the mainland
town of Bahía de Kino.
 The
objectives of the human use inventory are to:
1) quantify the level
of use according to user groups and activities, 2) determine which
months and seasons receive the highest levels of use, 3) to analyze
when high levels of use coincide with nesting seasons for the cormorants,
wading birds and gulls of the island, and 4) to evaluate whether
the close proximity of the island to a coastal population center
poses a heightened risk to the resources of the island.
The Human Use Inventory of
the Isla Alcatraz Program began in 2000 and continued until May
of 2003. Methods have been modified and improved slightly over time.
The methods described below describe those used most recently. Scientific
papers are available for all of the projects described here.
Methods
Direct observations of human use were made during pre-determined
periods. Observations were normally made with binoculars (12X50)
from the lighthouse located at the Northeast part of the island.
Observations were made seven days per month, beginning at 7:30 am
and continuing until 5:00 pm., and equally distributed throughout
the days of the week. No observations were made during the months
of July, August, or September. Each group was categorized into user
groups (tourists, fishermen, and researchers), and the activities,
numbers of people, and duration of stay for each group of visitors
were recorded on a data sheet. Activities conducted on the island
and those conducted in the waters near the shores of the island
were recorded on different data sheets. For the purposes of this
study, the island was divided into four offshore zones and four
onshore zones, and spatial use of the island by each group was recorded.
These zones did not cover the southern
section of the island that can only be accessed by boat. Human impacts
were also recorded, based on a human impact key that included levels
of bird disturbance; habitat alteration; and disposal of organic
waste, fecal matter, trash, and fishing gear. Boats that only past
by the island were recorded only if they caused a disturbance.
Results
A pilot project was instituted in the fall of 2000, the methods
of which were refined in a second project conducted from January
to April 2001. A total of 438 people in 96 groups were observed
visiting Isla Alcatraz during 165 hours of observation from January
to April. Tourists were the group most frequently observed visiting
the island. During Semana Santa, roughly 2.5 times more island use
was recorded than during the rest of the study period.
 During
this period human use was recorded in all zones. Sandy beach and
rocky substrate areas received the most overall use, undoubtedly
because they are the areas that visitors first encounter when coming
to the island by boat. Tourists were responsible for the largest
number of human impact incidents observed; these included disturbing
birds and altering habitat. The two most serious impacts observed
were caused by fishermen. The first occurred when a gill net drifted
onto the island's intertidal zone. At least 22 cormorants were caught
in the net as they pursued fish within its mesh. Although eight
of these were successfully extracted from the net, the remainder
drowned. The net was removed from the island by center researchers.
The second major incident (mentioned above) occurred when three
fishermen flushed several birds from the cormorant and wading bird
colonies, and removed a chuckwalla (Sauromalus varius,
an endemic to Islas San Esteban and Alcatraz) from the island. To
view results from this 2001 study click
here.
This project was continued
during the period from October 2001 through February 2002. During
this period only 52 hours of observations were made. Fishermen were
the group most frequently observed visitors to the island, followed
by tourists. Once again the sandy shores were the most frequently
visited areas. A more detailed analysis was made of the specific
locations visited by different user groups and of different activities
performed by different user groups. The frequency of different fishing
activities was also analyzed. To view results from this study click
here.
From March through May
of 2002 the project was continued with increased effort, totaling
253.5 hours of observation. During this period 616 visitors were
observed in 120 groups. Mexican tourists were the group most frequently
observed visiting the island. Once again the sandy shores in Zone
A received the most use by all user groups. Recreation was the most
frequent activity. The two alters on the island were frequently
visited by tourists. Tourists and researchers were the only groups
to visit the bird colonies. The most common human impacts were minor
bird disturbance and human waste deposition. The most serious impacts
occurred in March when tourists were observed collecting Yellow-footed
Gull eggs. To view results from this study click
here.
Between March of 2002
and February of 2003 we logged a total of 598.5 hours of observation,
during which the island was visited by 1056 people in 245 groups.
The average visit duration was 47 minutes. Visitors to the island
were predominantly of Mexican origin (84%). The majority of
the visitors to Isla Alcatraz were tourists (61%), followed by fishermen
(27%), researchers (5%), and others. Eighty-four percent of the
total time visitors spent on the island was in Zone A. Recreation,
including walking and bird-watching, was the most common activity
witnessed on the island (61%). The highest level of visitation
to the island occurred during the months of December, March, April
and May. The most common human impacts were minor bird disturbances
and trash deposition. There were 47 instances of major bird
disturbance during the study period. The waters adjacent to
the island were used by 1433 people in 357 groups, the majority
of which were fishermen and tourists. The most common activities
in the adjacent waters were recreation and commercial diving. To
review results of this study click here.
Significance of
project to program goals
Data collected to date provide a preliminary picture of total human
use of Isla Alcatraz, as well as spatial use trends and types of
use. The nesting season for the Double-crested Cormorant (September
- March) coincides with the period of lowest human use on the island.
The seven species of wading birds and the White Ibis nest from February
to June, and are therefore more vulnerable to high levels of human
disturbance. The impact on the Yellow-footed Gulls is even greater
because they nest in both the season and the zone of highest human
use of the island. This information can be used now to develop
management strategies. For example, the human impact data clearly
show that tourists visiting the island during the spring, and especially
during the high use period of Semana Santa, should be a priority
for education and outreach efforts. Regular trash clean ups
on the island is another strategy that could decrease the impact
to bird colonies. Overall, current levels of human use on
Isla Alcatraz do not cause grave threats to the nesting birds of
Alcatraz. With a few carefully implemented education programs,
impacts could be reduced even further.
 The
implementation of some basic management strategies regarding human
use has already begun. The week of Semana Santa has been identified
as a time of intensive human use on Isla Alcatraz. To help protect
nesting birds during Semana Santa 2001, a number of signs about
the ecology and the sensitivity of the birds were put up on the
island and on the beach in Bahía de Kino. These signs were
designed by members of the town’s seventh
grade ecology club, based on a survey they designed and circulated
to adult members of the community asking about their use of Isla
Alcatraz. During Semana Santa 2002 and 2003 Prescott College cooperated
with the Gulf Island
Reserve, to conduct an outreach operative with the purpose of
educating holiday users about the bird colonies and preventing them
from causing damage to the island flora and fauna.
Future work
Further work in the human use inventory is needed in the following
areas:
- continued periodic human use monitoring
- development of opportunities for increased participation within
the community of Bahía de Kino in the survey (such as those
carried out by the 7th grade ecology club students)
- use of the information already gained to implement management
strategies
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