We conducted a literature search for peer-reviewed publications, books and university theses, including factors related to marine ecotourism in Baja California and the states neighbouring the Gulf of California down to Puerto Vallarta, northwest Mexico. A factor ‘related’ to marine ecotourism is any measure which the authors of an article specifically link to the ecotourism industry, such as employment, economic metrics, tourism infrastructure, environmental status and variations thereof. We therefore define an ‘article’ as a published paper and a ‘study’ as an investigation of marine ecotourism or factors or variables related to marine ecotourism within a published paper. An article may therefore have more than one study within it if it addresses multiple ecotourism-related variables.

The literature search was undertaken using the commercial search engine Google Scholar, which indexes the full text of scholarly literature across an array of publishing formats. Combinations of the following general search terms were used: ‘marine’, ‘ecotourism’, ‘tourism’, ‘industry’, ‘holiday’, ‘vacation’, ‘recreation’, ‘economy’, ‘infrastructure’, ‘employment’, ‘environment’, ‘eco’, ‘nature’, along with a secondary search using terms related specifically to marine ecotourism activities in Mexico, including ‘diving’, ‘snorkelling’, ‘whale watching’, ‘shark watching’, ‘beach’, ‘kayak’, ‘sailing’, ‘cruise’, ‘fishing’, ‘angling’, ‘wildlife’, ‘national park’ and ‘protected area’. For a list of search combinations used and resultant internet ‘hits’ and numbers of peer-review journals for each, see Supplementary material Table S1. Google Scholar was chosen over Web of Science and Scopus as it gives a higher number of results per general search term (on average), covers non-ISI listed journals (a wider search base) and gives lower citation noise [lower citation variation (85% unique entries compared with ISI’s 60%)], which means that there are fewer replicated citations per search (Pauly and Stergiou 2005, Meho and Yang 2007).

The first one hundred search results from each keyword combination were examined, so a total of 2300 hits were evaluated for inclusion in the review (23 searches × 100 hits of each). From each article highlighted in the literature search, eight data variables were extracted and entered into a database (see Table 1 for details). In addition to categorical variables, brief one-sentence summaries of each article were made to allow discussion of more general, non-quantifiable patterns post-analysis and to increase the utility of the database resulting from the literature review.

We used ordinary least squares regression to investigate trends in the number of publications over time as well as the methods used within each and how the research focus has changed. It must be noted that the statistics described herein for each are casual tendencies as in all cases normality is violated but the data were not transformed in order to reduce the tendency to inflate type I error. The geographic distribution of the studies, years of publication, the subject organisms of the studies (if applicable) and the topic of focus (ecology vs economy vs social wellbeing) across Baja California was visualized using the Tableau 9.1 software. Finally, in order to elucidate the financial investments being made in marine ecotourism research in Baja California, we noted the agency types from which funding came for each publication reviewed (where specified).

Increased research effort over the 20 years reviewed is a promising trend, which, considering the potential of the Baja California Peninsula for ecotourism operations, the authors hope will continue. In particular, we believe that a continued effort to increase the amount of peer-reviewed output in the field will benefit the development of the marine ecotourism industry in a sustainable way, as it already has done, for example, in the formation of strict rules governing sighting programmes for whales (Heckel et al. 2003) and whale sharks (Cárdenas-Torres et al. 2007). Although theses made up approximately one third of all published materials reviewed, very few showed a similar publication rate for peer-reviewed articles. This could indicate a wasted research effort if, for example, NGOs or government agencies rely only on robust, peer-reviewed scientific output rather than student theses, whose rigour can be questioned more easily.

In terms of the study methodologies within the peer-reviewed publications, the increasing number of quantitative studies is also promising. Quantitative surveys likely give more strength to conclusions drawn from them than qualitative-only studies. They are also likely to be more directly usable in management applications, which often rely on numeric thresholds, such as carrying capacities of an area or the potential revenue of a given activity. The low numbers of studies employing modelling and GIS techniques is understandable as these are much newer analytical techniques than the other methods reviewed.

It is interesting to note that few studies on the Sonoran and Sinaloan coast were uncovered by our literature search. This paucity could be caused by a lack of research investment in these areas, a low number of marine ecotourism operations along these stretches of coast, or the fact that our literature search did not select these areas well using “Baja California” as a geographic search term. The south of the Baja Peninsula was comparatively well studied, with the majority of recent studies occurring in Cabo Pulmo and La Paz. This is likely due to the age of marine ecotourism operations in these areas based on the infrastructure (airports, road networks etc.) that has allowed rapid local growth. The spread of study type (ecology, economy and social wellbeing) across Baja California showed no distinct pattern, although it is clear that ecological publications dominate across the peninsula. Much of coastal Baja California and its surrounding waters are understudied, which is evident from the large stretches of coast for which no publications were found and the grouping of publications mainly around established towns and cities. This finding highlights a tendency for studies of marine ecotourism to be reports on extant operations rather than projections or predictions on the future potential of areas yet to be developed. This is something that would be beneficial to address, particularly in areas of ecological importance. In instances in which data already exist, development will be able to account for more than just potential revenue gains if information is freely available to stakeholders from the outset of a development proposal (e.g. Vanderplank et al. 2014).

The large number of publications studying or discussing whale sightseeing tourism were focused on the Pacific coast of the Baja California Peninsula, including the well-established ecotourism destination Laguna San Ignacio (Chong 2008, Rossing 2006). Being the most charismatic of the species noted, it is not surprising that whales (Gray and Humpback) were the largest of the organismal groups noted. The large number of studies concentrating on reef fish species are centred around the rocky reefs of the Cabo Pulmo National Park, as were the studies noting invertebrate species (Arizpe 2004). A 20-year closure to fishing has led to a 463% increase in fish biomass (Aburto-Oropeza et al. 2011) at Cabo Pulmo, which is now an important model system of successful ecotourism and marine conservation globally (Leslie et al. 2013). Surprisingly, only one of the studies highlighted in the literature search looked specifically at sports fishing in Baja California. Considering the general declining state of the Gulf of California’s fishing industry (Sala et al. 2004, Lluch-Cota et al. 2007) and the large number of sports fishing operators working from Baja California (Sievanen 2014), we expected more publications to detail the sports fishing industry as an economically viable alternative to traditional fishing (Barnett et al. 2015).

As mentioned above, we decided a priori that each study could be categorized into either ecological, economic or social wellbeing studies, or any combination of the three. Overall, a tendency towards ecology over economy over social wellbeing was clear. This pattern was also clear within papers that discussed a combination of two or all three of the study topic types, discussions of ecology taking precedence over economy and few analyses or conclusions regarding human social wellbeing. The lack of social wellbeing may, however, be a result of the relatively new industry of marine ecotourism in Baja California, which in some cases may mean that little social change has yet taken place since new operations were set up in certain areas. This, however, does not appear to be true for the more developed areas such as Cabo Pulmo, Cabo San Lucas and Ensenada, the locations of all of the social studies reviewed. The prevalence of ecological publications related to marine ecotourism in Baja California may well be attributed to the research objectives of the main funding bodies, all of which are ecology-based rather than economic or social science institutes / agencies [CONACYT (Consejo Nacional De Ciencia Y Tecnología), CICIMAR (Centro Interdisciplinario de Ciencias Marinas) and CICESE (Centro de Investigación Científica y Educación Superior de Ensenada)]. Mexican agencies have been the most prevalent funders of the publications highlighted in our review, most notably CONACYT.

Our comprehensive literature search allowed us to highlight some important trends and patterns in the field of marine ecotourism research in the Gulf of California and Baja California Peninsula, Mexico. It is, however, important to discuss possible limitations of our approach and the bearing they may have on our conclusions. This quantitative, systematic analysis included theses, books and conference papers. Although these three publication types do undergo some sort of peer-review process, it could be argued that it is not as stringent as that of peer-reviewed journal articles, which might invalidate some of the findings within the publications presented. Our analyses, however, are concerned with patterns in a field of research rather than scientific rigour.

Although the time period of publications we reviewed does not include anything earlier than 1994, this time period suitably captures regional research patterns; indeed, the literature search only highlighted one paper outside of this time frame (Anderson et al. 1976). Work by López-Espinosa de los Monteros (2002) also indicates that ecotourism in the southern Baja California Peninsula began following this period. Although we used a comprehensive, quantitative approach to select relevant publications, it is impossible to say that the literature search is exhaustive. There are likely to be articles that were missed by the search term combinations we chose or have never made it into mainstream search-engine territory. Finally, it must be noted what truly classifies “marine” in our review. One fifth of all of the publications included in the review actually discuss what may be classified as terrestrial ecotourism instead of marine-based activities. Such publications were, however, kept in the analysis if they linked strongly with marine systems (e.g. coastal wetlands or sea cliffs) or the main discussion in the publication also drew conclusions relating directly to marine systems (e.g. effluent from hotels running into marine systems).

It is also important to mention the robustness of our analysis of trends using ordinary least squares regressions. Although the method is appropriate for the analysis of linear trends, a lack of data in some instances means that our interpretations must be taken with caution. For example, the statistical significance of regressions that were run with few (e.g. less than 10) points is based on a small sample size and may therefore not be wholly representative of the existence or absence of real-world trends. Unfortunately, because of the lack of data for some of the regressions run, this problem cannot be overcome. The lack of data does, however, highlight the fact that, for example, there have been few GIS studies of ecotourism in Baja California for the time period analysed. Overall, however, we believe that our literature review methodology captures the field of research publications relating to marine ecotourism in Baja California well, and provides important information relating to patterns in the field and future areas for development.

Our review highlights some interesting patterns in the research effort relating to marine ecotourism in Baja California and the Gulf of California. However, there are multiple research areas in this field that could be bolstered to provide a more complete analysis of this industry. For example, theses form an important part of the total literature yet few have been published in peer-reviewed journals. Promoting the publication of theses in peer-reviewed publications may give their findings more weight in potential management decisions and a wider audience in general. In addition, there are few current modelling and GIS-specific studies of marine ecotourism in Baja California. Investing more research effort in predictive modelling studies and GIS outputs for use by resource managers (predicted, future quantities and map layers) will likely yield beneficial results.

A common theme in publication conclusions is the need for collaboration and involvement from all stakeholder groups. Collaborations between stakeholders and the research community will be strengthened if research actively incorporates stakeholders into research and reports findings back to those groups affected by the industries under study. For instance, sport fishing is under-represented in the literature as an ecotourism activity, yet makes up an important part of Baja California’s ecotourism (Cisneros-Montemayor et al. 2012). More research outputs relating to the commercial and recreational fishing sector from the ecological, economic and social wellbeing perspectives would inform both the tourists taking part in such activities and the commercial fishers in these regions, who may consider converting to sports fishing operations if commercial catches in the Gulf continue to show signs of overexploitation (Sala et al. 2004).

Finally, there are many coastal areas in Baja California and the Gulf of California that appear never to have been studied. As tourism and human populations throughout the region continue to grow (Agersted 2006, Center for Responsible Travel 2017), it is important to have information, data and opinions ready for development committees wishing to transform areas of Baja California into holiday hotspots. Pre-development studies will be hugely beneficial in informing stakeholders but must be directed at areas of promise that are likely to be subject to development in the coming years. While overall ecology dominates the literature over economy and social studies, future studies that incorporate the fields of economy and human social wellbeing would provide managers with a more complete suite of information relating to Baja California’s marine ecotourism development.